1 .. SPDX-License-Identifier: GPL-2.0+
3 Compiled-in Device Tree / Platform Data
4 =======================================
10 Device tree is the standard configuration method in U-Boot. It is used to
11 define what devices are in the system and provide configuration information
14 The overhead of adding devicetree access to U-Boot is fairly modest,
15 approximately 3KB on Thumb 2 (plus the size of the DT itself). This means
16 that in most cases it is best to use devicetree for configuration.
18 However there are some very constrained environments where U-Boot needs to
19 work. These include SPL with severe memory limitations. For example, some
20 SoCs require a 16KB SPL image which must include a full MMC stack. In this
21 case the overhead of devicetree access may be too great.
23 It is possible to create platform data manually by defining C structures
24 for it, and reference that data in a `U_BOOT_DRVINFO()` declaration. This
25 bypasses the use of devicetree completely, effectively creating a parallel
26 configuration mechanism. But it is an available option for SPL.
28 As an alternative, the 'of-platdata' feature is provided. This converts the
29 devicetree contents into C code which can be compiled into the SPL binary.
30 This saves the 3KB of code overhead and perhaps a few hundred more bytes due
31 to more efficient storage of the data.
37 The feature is enabled by CONFIG OF_PLATDATA. This is only available in
38 SPL/TPL and should be tested with:
42 #if CONFIG_IS_ENABLED(OF_PLATDATA)
44 A tool called 'dtoc' converts a devicetree file either into a set of
45 struct declarations, one for each compatible node, and a set of
46 `U_BOOT_DRVINFO()` declarations along with the actual platform data for each
47 device. As an example, consider this MMC node:
51 sdmmc: dwmmc@ff0c0000 {
52 compatible = "rockchip,rk3288-dw-mshc";
53 clock-freq-min-max = <400000 150000000>;
54 clocks = <&cru HCLK_SDMMC>, <&cru SCLK_SDMMC>,
55 <&cru SCLK_SDMMC_DRV>, <&cru SCLK_SDMMC_SAMPLE>;
56 clock-names = "biu", "ciu", "ciu_drv", "ciu_sample";
58 interrupts = <GIC_SPI 32 IRQ_TYPE_LEVEL_HIGH>;
59 reg = <0xff0c0000 0x4000>;
63 card-detect-delay = <200>;
66 pinctrl-names = "default";
67 pinctrl-0 = <&sdmmc_clk>, <&sdmmc_cmd>, <&sdmmc_cd>, <&sdmmc_bus4>;
68 vmmc-supply = <&vcc_sd>;
74 Some of these properties are dropped by U-Boot under control of the
75 CONFIG_OF_SPL_REMOVE_PROPS option. The rest are processed. This will produce
76 the following C struct declaration:
80 struct dtd_rockchip_rk3288_dw_mshc {
82 bool cap_mmc_highspeed;
83 bool cap_sd_highspeed;
84 fdt32_t card_detect_delay;
85 fdt32_t clock_freq_min_max[2];
86 struct phandle_1_arg clocks[4];
89 fdt32_t interrupts[3];
95 and the following device declarations:
99 /* Node /clock-controller@ff760000 index 0 */
102 /* Node /dwmmc@ff0c0000 index 2 */
103 static struct dtd_rockchip_rk3288_dw_mshc dtv_dwmmc_at_ff0c0000 = {
105 .cap_sd_highspeed = true,
106 .interrupts = {0x0, 0x20, 0x4},
107 .clock_freq_min_max = {0x61a80, 0x8f0d180},
114 .cap_mmc_highspeed = true,
117 .u_boot_dm_pre_reloc = true,
118 .reg = {0xff0c0000, 0x4000},
119 .card_detect_delay = 0xc8,
122 U_BOOT_DRVINFO(dwmmc_at_ff0c0000) = {
123 .name = "rockchip_rk3288_dw_mshc",
124 .plat = &dtv_dwmmc_at_ff0c0000,
125 .plat_size = sizeof(dtv_dwmmc_at_ff0c0000),
129 The device is then instantiated at run-time and the platform data can be
135 struct dtd_rockchip_rk3288_dw_mshc *plat = dev_get_plat(dev);
137 This avoids the code overhead of converting the devicetree data to
138 platform data in the driver. The `of_to_plat()` method should
139 therefore do nothing in such a driver.
141 Note that for the platform data to be matched with a driver, the 'name'
142 property of the `U_BOOT_DRVINFO()` declaration has to match a driver declared
143 via `U_BOOT_DRIVER()`. This effectively means that a `U_BOOT_DRIVER()` with a
144 'name' corresponding to the devicetree 'compatible' string (after converting
145 it to a valid name for C) is needed, so a dedicated driver is required for
146 each 'compatible' string.
148 In order to make this a bit more flexible, the `DM_DRIVER_ALIAS()` macro can be
149 used to declare an alias for a driver name, typically a 'compatible' string.
150 This macro produces no code, but is used by dtoc tool. It must be located in the
151 same file as its associated driver, ideally just after it.
153 The parent_idx is the index of the parent `driver_info` structure within its
154 linker list (instantiated by the `U_BOOT_DRVINFO()` macro). This is used to
155 support `dev_get_parent()`.
157 During the build process dtoc parses both `U_BOOT_DRIVER()` and
158 `DM_DRIVER_ALIAS()` to build a list of valid driver names and driver aliases.
159 If the 'compatible' string used for a device does not not match a valid driver
160 name, it will be checked against the list of driver aliases in order to get the
161 right driver name to use. If in this step there is no match found a warning is
162 issued to avoid run-time failures.
164 Where a node has multiple compatible strings, dtoc generates a `#define` to
165 make them equivalent, e.g.:
169 #define dtd_rockchip_rk3299_dw_mshc dtd_rockchip_rk3288_dw_mshc
172 Converting of-platdata to a useful form
173 ---------------------------------------
175 Of course it would be possible to use the of-platdata directly in your driver
176 whenever configuration information is required. However this means that the
177 driver will not be able to support devicetree, since the of-platdata
178 structure is not available when devicetree is used. It would make no sense
179 to use this structure if devicetree were available, since the structure has
180 all the limitations metioned in caveats below.
182 Therefore it is recommended that the of-platdata structure should be used
183 only in the `probe()` method of your driver. It cannot be used in the
184 `of_to_plat()` method since this is not called when platform data is
188 How to structure your driver
189 ----------------------------
191 Drivers should always support devicetree as an option. The of-platdata
192 feature is intended as a add-on to existing drivers.
194 Your driver should convert the plat struct in its `probe()` method. The
195 existing devicetree decoding logic should be kept in the
196 `of_to_plat()` method and wrapped with `#if`.
202 #include <dt-structs.h>
205 #if CONFIG_IS_ENABLED(OF_PLATDATA)
206 /* Put this first since driver model will copy the data here */
207 struct dtd_mmc dtplat;
210 * Other fields can go here, to be filled in by decoding from
211 * the devicetree (or the C structures when of-platdata is used).
216 static int mmc_of_to_plat(struct udevice *dev)
218 if (CONFIG_IS_ENABLED(OF_REAL)) {
219 /* Decode the devicetree data */
220 struct mmc_plat *plat = dev_get_plat(dev);
221 const void *blob = gd->fdt_blob;
222 int node = dev_of_offset(dev);
224 plat->fifo_depth = fdtdec_get_int(blob, node, "fifo-depth", 0);
230 static int mmc_probe(struct udevice *dev)
232 struct mmc_plat *plat = dev_get_plat(dev);
234 #if CONFIG_IS_ENABLED(OF_PLATDATA)
235 /* Decode the of-platdata from the C structures */
236 struct dtd_mmc *dtplat = &plat->dtplat;
238 plat->fifo_depth = dtplat->fifo_depth;
240 /* Set up the device from the plat data */
241 writel(plat->fifo_depth, ...)
244 static const struct udevice_id mmc_ids[] = {
245 { .compatible = "vendor,mmc" },
249 U_BOOT_DRIVER(mmc_drv) = {
253 .of_to_plat = mmc_of_to_plat,
255 .priv_auto = sizeof(struct mmc_priv),
256 .plat_auto = sizeof(struct mmc_plat),
259 DM_DRIVER_ALIAS(mmc_drv, vendor_mmc) /* matches compatible string */
261 Note that `struct mmc_plat` is defined in the C file, not in a header. This
262 is to avoid needing to include dt-structs.h in a header file. The idea is to
263 keep the use of each of-platdata struct to the smallest possible code area.
264 There is just one driver C file for each struct, that can convert from the
265 of-platdata struct to the standard one used by the driver.
267 In the case where SPL_OF_PLATDATA is enabled, `plat_auto` is
268 still used to allocate space for the platform data. This is different from
269 the normal behaviour and is triggered by the use of of-platdata (strictly
270 speaking it is a non-zero `plat_size` which triggers this).
272 The of-platdata struct contents is copied from the C structure data to the
273 start of the newly allocated area. In the case where devicetree is used,
274 the platform data is allocated, and starts zeroed. In this case the
275 `of_to_plat()` method should still set up the platform data (and the
276 of-platdata struct will not be present).
278 SPL must use either of-platdata or devicetree. Drivers cannot use both at
279 the same time, but they must support devicetree. Supporting of-platdata is
282 The devicetree becomes inaccessible when CONFIG_SPL_OF_PLATDATA is enabled,
283 since the devicetree access code is not compiled in. A corollary is that
284 a board can only move to using of-platdata if all the drivers it uses support
285 it. There would be little point in having some drivers require the device
286 tree data, since then libfdt would still be needed for those drivers and
287 there would be no code-size benefit.
290 Build-time instantiation
291 ------------------------
293 Even with of-platdata there is a fair amount of code required in driver model.
294 It is possible to have U-Boot handle the instantiation of devices at build-time,
295 so avoiding the need for the `device_bind()` code and some parts of
298 The feature is enabled by CONFIG_OF_PLATDATA_INST.
300 Here is an example device, as generated by dtoc::
303 * Node /serial index 6
304 * driver sandbox_serial parent root_driver
307 #include <asm/serial.h>
308 struct sandbox_serial_plat __attribute__ ((section (".priv_data")))
309 _sandbox_serial_plat_serial = {
311 .sandbox_text_colour = "cyan",
314 #include <asm/serial.h>
315 u8 _sandbox_serial_priv_serial[sizeof(struct sandbox_serial_priv)]
316 __attribute__ ((section (".priv_data")));
318 u8 _sandbox_serial_uc_priv_serial[sizeof(struct serial_dev_priv)]
319 __attribute__ ((section (".priv_data")));
321 DM_DEVICE_INST(serial) = {
322 .driver = DM_DRIVER_REF(sandbox_serial),
323 .name = "sandbox_serial",
324 .plat_ = &_sandbox_serial_plat_serial,
325 .priv_ = _sandbox_serial_priv_serial,
326 .uclass = DM_UCLASS_REF(serial),
327 .uclass_priv_ = _sandbox_serial_uc_priv_serial,
329 .prev = &DM_UCLASS_REF(serial)->dev_head,
330 .next = &DM_UCLASS_REF(serial)->dev_head,
333 .prev = &DM_DEVICE_REF(serial)->child_head,
334 .next = &DM_DEVICE_REF(serial)->child_head,
337 .prev = &DM_DEVICE_REF(i2c_at_0)->sibling_node,
338 .next = &DM_DEVICE_REF(spl_test)->sibling_node,
343 Here is part of the driver, for reference::
345 static const struct udevice_id sandbox_serial_ids[] = {
346 { .compatible = "sandbox,serial" },
350 U_BOOT_DRIVER(sandbox_serial) = {
351 .name = "sandbox_serial",
353 .of_match = sandbox_serial_ids,
354 .of_to_plat = sandbox_serial_of_to_plat,
355 .plat_auto = sizeof(struct sandbox_serial_plat),
356 .priv_auto = sizeof(struct sandbox_serial_priv),
357 .probe = sandbox_serial_probe,
358 .remove = sandbox_serial_remove,
359 .ops = &sandbox_serial_ops,
360 .flags = DM_FLAG_PRE_RELOC,
364 The `DM_DEVICE_INST()` macro declares a struct udevice so you can see that the
365 members are from that struct. The private data is declared immediately above,
366 as `_sandbox_serial_priv_serial`, so there is no need for run-time memory
367 allocation. The #include lines are generated as well, since dtoc searches the
368 U-Boot source code for the definition of `struct sandbox_serial_priv` and adds
369 the relevant header so that the code will compile without errors.
371 The `plat_` member is set to the dtv data which is declared immediately above
372 the device. This is similar to how it would look without of-platdata-inst, but
373 node that the `dtplat` member inside is part of the wider
374 `_sandbox_serial_plat_serial` struct. This is because the driver declares its
375 own platform data, and the part generated by dtoc can only be a portion of it.
376 The `dtplat` part is always first in the struct. If the device has no
377 `.plat_auto` field, then a simple dtv struct can be used as with this example::
379 static struct dtd_sandbox_clk dtv_clk_sbox = {
380 .assigned_clock_rates = 0x141,
381 .assigned_clocks = {0x7, 0x3},
385 u8 _sandbox_clk_priv_clk_sbox[sizeof(struct sandbox_clk_priv)]
386 __attribute__ ((section (".priv_data")));
388 DM_DEVICE_INST(clk_sbox) = {
389 .driver = DM_DRIVER_REF(sandbox_clk),
390 .name = "sandbox_clk",
391 .plat_ = &dtv_clk_sbox,
393 Here is part of the driver, for reference::
395 static const struct udevice_id sandbox_clk_ids[] = {
396 { .compatible = "sandbox,clk" },
400 U_BOOT_DRIVER(sandbox_clk) = {
401 .name = "sandbox_clk",
403 .of_match = sandbox_clk_ids,
404 .ops = &sandbox_clk_ops,
405 .probe = sandbox_clk_probe,
406 .priv_auto = sizeof(struct sandbox_clk_priv),
410 You can see that `dtv_clk_sbox` just has the devicetree contents and there is
411 no need for the `dtplat` separation, since the driver has no platform data of
412 its own, besides that provided by the devicetree (i.e. no `.plat_auto` field).
414 The doubly linked lists are handled by explicitly declaring the value of each
415 node, as you can see with the `.prev` and `.next` values in the example above.
416 Since dtoc knows the order of devices it can link them into the appropriate
419 One of the features of driver model is the ability for a uclass to have a
420 small amount of private data for each device in that uclass. This is used to
421 provide a generic data structure that the uclass can use for all devices, thus
422 allowing generic features to be implemented in common code. An example is I2C,
423 which stores the bus speed there.
425 Similarly, parent devices can have data associated with each of their children.
426 This is used to provide information common to all children of a particular bus.
427 For an I2C bus, this is used to store the I2C address of each child on the bus.
429 This is all handled automatically by dtoc::
432 u8 _sandbox_i2c_priv_i2c_at_0[sizeof(struct sandbox_i2c_priv)]
433 __attribute__ ((section (".priv_data")));
435 u8 _sandbox_i2c_uc_priv_i2c_at_0[sizeof(struct dm_i2c_bus)]
436 __attribute__ ((section (".priv_data")));
438 DM_DEVICE_INST(i2c_at_0) = {
439 .driver = DM_DRIVER_REF(sandbox_i2c),
440 .name = "sandbox_i2c",
441 .plat_ = &dtv_i2c_at_0,
442 .priv_ = _sandbox_i2c_priv_i2c_at_0,
443 .uclass = DM_UCLASS_REF(i2c),
444 .uclass_priv_ = _sandbox_i2c_uc_priv_i2c_at_0,
447 Part of driver, for reference::
449 static const struct udevice_id sandbox_i2c_ids[] = {
450 { .compatible = "sandbox,i2c" },
454 U_BOOT_DRIVER(sandbox_i2c) = {
455 .name = "sandbox_i2c",
457 .of_match = sandbox_i2c_ids,
458 .ops = &sandbox_i2c_ops,
459 .priv_auto = sizeof(struct sandbox_i2c_priv),
462 Part of I2C uclass, for reference::
464 UCLASS_DRIVER(i2c) = {
467 .flags = DM_UC_FLAG_SEQ_ALIAS,
468 .post_bind = i2c_post_bind,
469 .pre_probe = i2c_pre_probe,
470 .post_probe = i2c_post_probe,
471 .per_device_auto = sizeof(struct dm_i2c_bus),
472 .per_child_plat_auto = sizeof(struct dm_i2c_chip),
473 .child_post_bind = i2c_child_post_bind,
476 Here, `_sandbox_i2c_uc_priv_i2c_at_0` is required by the uclass but is declared
477 in the device, as required by driver model. The required header file is included
478 so that the code will compile without errors. A similar mechanism is used for
479 child devices, but is not shown by this example.
481 It would not be that useful to avoid binding devices but still need to allocate
482 uclasses at runtime. So dtoc generates uclass instances as well::
484 struct list_head uclass_head = {
485 .prev = &DM_UCLASS_REF(serial)->sibling_node,
486 .next = &DM_UCLASS_REF(clk)->sibling_node,
489 DM_UCLASS_INST(clk) = {
490 .uc_drv = DM_UCLASS_DRIVER_REF(clk),
492 .prev = &uclass_head,
493 .next = &DM_UCLASS_REF(i2c)->sibling_node,
496 .prev = &DM_DEVICE_REF(clk_sbox)->uclass_node,
497 .next = &DM_DEVICE_REF(clk_fixed)->uclass_node,
501 At the top is the list head. Driver model uses this on start-up, instead of
504 Below that are a set of `DM_UCLASS_INST()` macros, each declaring a
505 `struct uclass`. The doubly linked lists work as for devices.
507 All private data is placed into a `.priv_data` section so that it is contiguous
508 in the resulting output binary.
514 U-Boot stores drivers, devices and many other things in linker_list structures.
515 These are sorted by name, so dtoc knows the order that they will appear when
516 the linker runs. Each driver_info / udevice is referenced by its index in the
517 linker_list array, called 'idx' in the code.
519 When CONFIG_OF_PLATDATA_INST is enabled, idx is the udevice index, otherwise it
520 is the driver_info index. In either case, indexes are used to reference devices
521 using device_get_by_ofplat_idx(). This allows phandles to work as expected.
527 U-Boot operates in several phases, typically TPL, SPL and U-Boot proper.
528 The latter does not use dtoc.
530 In some rare cases different drivers are used for two phases. For example,
531 in TPL it may not be necessary to use the full PCI subsystem, so a simple
532 driver can be used instead.
534 This works in the build system simply by compiling in one driver or the
535 other (e.g. PCI driver + uclass for SPL; simple_bus for TPL). But dtoc has
536 no way of knowing which code is compiled in for which phase, since it does
537 not inspect Makefiles or dependency graphs.
539 So to make this work for dtoc, we need to be able to explicitly mark
540 drivers with their phase. This is done by adding a macro to the driver::
542 /* code in tpl.c only compiled into TPL */
543 U_BOOT_DRIVER(pci_x86) = {
545 .id = UCLASS_SIMPLE_BUS,
546 .of_match = of_match_ptr(tpl_fake_pci_ids),
551 /* code in pci_x86.c compiled into SPL and U-Boot proper */
552 U_BOOT_DRIVER(pci_x86) = {
555 .of_match = pci_x86_ids,
560 Notice that the second driver has the same name but no DM_PHASE(), so it will be
561 used for SPL and U-Boot.
563 Note also that this only affects the code generated by dtoc. You still need to
564 make sure that only the required driver is build into each phase.
570 With OF_PLATDATA_INST, dtoc must include the correct header file in the
571 generated code for any structs that are used, so that the code will compile.
572 For example, if `struct ns16550_plat` is used, the code must include the
573 `ns16550.h` header file.
575 Typically dtoc can detect the header file needed for a driver by looking
576 for the structs that it uses. For example, if a driver as a `.priv_auto`
577 that uses `struct ns16550_plat`, then dtoc can search header files for the
578 definition of that struct and use the file.
580 In some cases, enums are used in drivers, typically with the `.data` field
581 of `struct udevice_id`. Since dtoc does not support searching for these,
582 you must use the `DM_HDR()` macro to tell dtoc which header to use. This works
583 as a macro included in the driver definition::
585 static const struct udevice_id apl_syscon_ids[] = {
586 { .compatible = "intel,apl-punit", .data = X86_SYSCON_PUNIT },
590 U_BOOT_DRIVER(intel_apl_punit) = {
591 .name = "intel_apl_punit",
593 .of_match = apl_syscon_ids,
594 .probe = apl_punit_probe,
595 DM_HEADER(<asm/cpu.h>) /* for X86_SYSCON_PUNIT */
603 This section shows some common problems and how to fix them.
608 In some cases you will you see something like this::
610 WARNING: the driver rockchip_rk3188_grf was not found in the driver list
612 The driver list is a list of drivers, each with a name. The name is in the
613 U_BOOT_DRIVER() declaration, repeated twice, one in brackets and once as the
614 .name member. For example, in the following declaration the driver name is
615 `rockchip_rk3188_grf`::
617 U_BOOT_DRIVER(rockchip_rk3188_grf) = {
618 .name = "rockchip_rk3188_grf",
620 .of_match = rk3188_syscon_ids + 1,
621 .bind = rk3188_syscon_bind_of_plat,
624 The first name U_BOOT_DRIVER(xx) is used to create a linker symbol so that the
625 driver can be accessed at build-time without any overhead. The second one
626 (.name = "xx") is used at runtime when something wants to print out the driver
629 The dtoc tool expects to be able to find a driver for each compatible string in
630 the devicetree. For example, if the devicetree has::
633 compatible = "rockchip,rk3188-grf", "syscon";
634 reg = <0x20008000 0x200>;
638 then dtoc looks at the first compatible string ("rockchip,rk3188-grf"),
639 converts that to a C identifier (rockchip_rk3188_grf) and then looks for that.
641 Missing .compatible or Missing .id
642 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
644 Various things can cause dtoc to fail to find the driver and it tries to
645 warn about these. For example:
647 rockchip_rk3188_uart: Missing .compatible in drivers/serial/serial_rockchip.c
648 : WARNING: the driver rockchip_rk3188_uart was not found in the driver list
650 Without a compatible string a driver cannot be used by dtoc, even if the
651 compatible string is not actually needed at runtime.
653 If the problem is simply that there are multiple compatible strings, the
654 DM_DRIVER_ALIAS() macro can be used to tell dtoc about this and avoid a problem.
656 Checks are also made to confirm that the referenced driver has a .compatible
657 member and a .id member. The first provides the array of compatible strings and
658 the second provides the uclass ID.
663 When a device is used, its parent must be present as well. If you see an error
666 Node '/i2c@0/emul/emul0' requires parent node '/i2c@0/emul' but it is not in
669 it indicates that you are using a node whose parent is not present in the
670 devicetree. In this example, if you look at the device tree output
671 (e.g. fdtdump tpl/u-boot-tpl.dtb in your build directory), you may see something
676 compatible = "sandbox,i2c-rtc-emul";
677 #emul-cells = <0x00000000>;
678 phandle = <0x00000003>;
682 In this example, 'emul0' exists but its parent 'emul' has no properties. These
683 have been dropped by fdtgrep in an effort to reduce the devicetree size. This
684 indicates that the two nodes have different phase settings. Looking at the
690 compatible = "sandbox,i2c-emul-parent";
693 compatible = "sandbox,i2c-rtc-emul";
698 you can see that the child node 'emul0' usees 'u-boot,dm-pre-reloc', indicating
699 that the node is present in all SPL builds, but its parent uses 'u-boot,dm-spl'
700 indicating it is only present in SPL, not TPL. For a TPL build, this will fail
701 with the above message. The fix is to change 'emul0' to use the same
702 'u-boot,dm-spl' condition, so that it is not present in TPL, like its parent.
704 Link errors / undefined reference
705 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
707 Sometimes dtoc does not find the problem for you, but something is wrong and
708 you get a link error, e.g.::
710 :(.u_boot_list_2_udevice_2_spl_test5+0x0): undefined reference to
711 `_u_boot_list_2_driver_2_sandbox_spl_test'
712 /usr/bin/ld: dts/dt-uclass.o:(.u_boot_list_2_uclass_2_misc+0x8):
713 undefined reference to `_u_boot_list_2_uclass_driver_2_misc'
715 The first one indicates that the device cannot find its driver. This means that
716 there is a driver 'sandbox_spl_test' but it is not compiled into the build.
717 Check your Kconfig settings to make sure it is. If you don't want that in the
718 build, adjust your phase settings, e.g. by using 'u-boot,dm-spl' in the node
719 to exclude it from the TPL build::
723 compatible = "sandbox,spl-test";
727 We can drop the 'u-boot,dm-tpl' line so this node won't appear in the TPL
728 devicetree and thus the driver won't be needed.
730 The second error above indicates that the MISC uclass is needed by the driver
731 (since it is in the MISC uclass) but that uclass is not compiled in the build.
732 The fix above would fix this error too. But if you do want this uclass in the
733 build, check your Kconfig settings to make sure the uclass is being built
734 (CONFIG_MISC in this case).
740 There are various complications with this feature which mean it should only
741 be used when strictly necessary, i.e. in SPL with limited memory. Notable
744 - Device tree does not describe data types. But the C code must define a
745 type for each property. These are guessed using heuristics which
746 are wrong in several fairly common cases. For example an 8-byte value
747 is considered to be a 2-item integer array, and is byte-swapped. A
748 boolean value that is not present means 'false', but cannot be
749 included in the structures since there is generally no mention of it
750 in the devicetree file.
752 - Naming of nodes and properties is automatic. This means that they follow
753 the naming in the devicetree, which may result in C identifiers that
756 - It is not possible to find a value given a property name. Code must use
757 the associated C member variable directly in the code. This makes
758 the code less robust in the face of devicetree changes. To avoid having
759 a second struct with similar members and names you need to explicitly
760 declare it as an alias with `DM_DRIVER_ALIAS()`.
762 - The platform data is provided to drivers as a C structure. The driver
763 must use the same structure to access the data. Since a driver
764 normally also supports devicetree it must use `#ifdef` to separate
765 out this code, since the structures are only available in SPL. This could
766 be fixed fairly easily by making the structs available outside SPL, so
767 that `IS_ENABLED()` could be used.
769 - With CONFIG_OF_PLATDATA_INST all binding happens at build-time, meaning
770 that (by default) it is not possible to call `device_bind()` from C code.
771 This means that all devices must have an associated devicetree node and
772 compatible string. For example if a GPIO device currently creates child
773 devices in its `bind()` method, it will not work with
774 CONFIG_OF_PLATDATA_INST. Arguably this is bad practice anyway and the
775 devicetree binding should be updated to declare compatible strings for
776 the child devices. It is possible to disable OF_PLATDATA_NO_BIND but this
777 is not recommended since it increases code size.
786 When enabled, dtoc generates the following five files:
788 include/generated/dt-decl.h (OF_PLATDATA_INST only)
789 Contains declarations for all drivers, devices and uclasses. This allows
790 any `struct udevice`, `struct driver` or `struct uclass` to be located by its
793 include/generated/dt-structs-gen.h
794 Contains the struct definitions for the devicetree nodes that are used. This
795 is the same as without OF_PLATDATA_INST
797 spl/dts/dt-plat.c (only with !OF_PLATDATA_INST)
798 Contains the `U_BOOT_DRVINFO()` declarations that U-Boot uses to bind devices
799 at start-up. See above for an example
801 spl/dts/dt-device.c (only with OF_PLATDATA_INST)
802 Contains `DM_DEVICE_INST()` declarations for each device that can be used at
803 run-time. These are declared in the file along with any private/platform data
804 that they use. Every device has an idx, as above. Since each device must be
805 part of a double-linked list, the nodes are declared in the code as well.
807 spl/dts/dt-uclass.c (only with OF_PLATDATA_INST)
808 Contains `DM_UCLASS_INST()` declarations for each uclass that can be used at
809 run-time. These are declared in the file along with any private data
810 associated with the uclass itself (the `.priv_auto` member). Since each
811 uclass must be part of a double-linked list, the nodes are declared in the
814 The dt-structs.h file includes the generated file
815 `(include/generated/dt-structs.h`) if CONFIG_SPL_OF_PLATDATA is enabled.
816 Otherwise (such as in U-Boot proper) these structs are not available. This
817 prevents them being used inadvertently. All usage must be bracketed with
818 `#if CONFIG_IS_ENABLED(OF_PLATDATA)`.
820 The dt-plat.c file contains the device declarations and is is built in
827 Several CONFIG options are used to control the behaviour of of-platdata, all
828 available for both SPL and TPL:
831 This is the main option which enables the of-platdata feature
834 This allows `device_get_parent()` to work. Without this, all devices exist as
835 direct children of the root node. This option is highly desirable (if not
836 always absolutely essential) for buses such as I2C.
839 This controls the instantiation of devices at build time. With it disabled,
840 only `U_BOOT_DRVINFO()` records are created, with U-Boot handling the binding
841 in `device_bind()` on start-up. With it enabled, only `DM_DEVICE_INST()` and
842 `DM_UCLASS_INST()` records are created, and `device_bind()` is not needed at
846 This controls whether `device_bind()` is supported. It is enabled by default
847 with OF_PLATDATA_INST since code-size reduction is really the main point of
848 the feature. It can be disabled if needed but is not likely to be supported
851 OF_PLATDATA_DRIVER_RT
852 This controls whether the `struct driver_rt` records are used by U-Boot.
853 Normally when a device is bound, U-Boot stores the device pointer in one of
854 these records. There is one for every `struct driver_info` in the system,
855 i.e. one for every device that is bound from those records. It provides a
856 way to locate a device in the code and is used by
857 `device_get_by_ofplat_idx()`. This option is always enabled with of-platdata,
858 provided OF_PLATDATA_INST is not. In that case the records are useless since
859 we don't have any `struct driver_info` records.
862 This controls whether the `struct udevice_rt` records are used by U-Boot.
863 It moves the updatable fields from `struct udevice` (currently only `flags`)
864 into a separate structure, allowing the records to be kept in read-only
865 memory. It is generally enabled if OF_PLATDATA_INST is enabled. This option
866 also controls whether the private data is used in situ, or first copied into
867 an allocated region. Again this is to allow the private data declared by
868 dtoc-generated code to be in read-only memory. Note that access to private
869 data must be done via accessor functions, such as `dev_get_priv()`, so that
870 the relocation is handled.
873 This indicates that the data generated by dtoc should not be modified. Only
874 a few fields actually do get changed in U-Boot, such as device flags. This
875 option causes those to move into an allocated space (see OF_PLATDATA_RT).
876 Also, since updating doubly linked lists is generally impossible when some of
877 the nodes cannot be updated, OF_PLATDATA_NO_BIND is enabled.
882 A few extra data structures are used with of-platdata:
885 Run-time information for devices. When OF_PLATDATA_RT is enabled, this holds
886 the flags for each device, so that `struct udevice` can remain unchanged by
887 U-Boot, and potentially reside in read-only memory. Access to flags is then
888 via functions like `dev_get_flags()` and `dev_or_flags()`. This data
889 structure is allocated on start-up, where the private data is also copied.
890 All flags values start at 0 and any changes are handled by `dev_or_flags()`
891 and `dev_bic_flags()`. It would be more correct for the flags to be set to
892 `DM_FLAG_BOUND`, or perhaps `DM_FLAG_BOUND | DM_FLAG_ALLOC_PDATA`, but since
893 there is no code to bind/unbind devices and no code to allocate/free
894 private data / platform data, it doesn't matter.
897 Run-time information for `struct driver_info` records. When
898 OF_PLATDATA_DRIVER_RT is enabled, this holds a pointer to the device
899 created by each record. This is needed so that is it possible to locate a
900 device from C code. Specifically, the code can use `DM_DRVINFO_GET(name)` to
901 get a reference to a particular `struct driver_info`, with `name` being the
902 name of the devicetree node. This is very convenient. It is also fast, since
903 no searching or string comparison is needed. This data structure is
904 allocated on start-up, filled out by `device_bind()` and used by
905 `device_get_by_ofplat_idx()`.
910 Some other changes are made with of-platdata:
913 Accessing private / platform data via functions such as `dev_get_priv()` has
914 always been encouraged. With OF_PLATDATA_RT this is essential, since the
915 `priv_` and `plat_` (etc.) values point to the data generated by dtoc, not
916 the read-write copy that is sometimes made on start-up. Changing the
917 private / platform data pointers has always been discouraged (the API is
918 marked internal) but with OF_PLATDATA_RT this is not currently supported in
919 general, since it assumes that all such pointers point to the relocated data.
920 Note also that the renaming of struct members to have a trailing underscore
921 was partly done to make people aware that they should not be accessed
925 Normally U-Boot sets up the head of the uclass list here and makes
926 `gd->uclass_root` point to it. With OF_PLATDATA_INST, dtoc generates a
927 declaration of `uclass_head` in `dt-uclass.c` since it needs to link the
928 head node into the list. In that case, `gd->uclass_root_s` is not used and
929 U-Boot just makes `gd->uclass_root` point to `uclass_head`.
932 This holds a pointer to a list of `struct driver_rt` records, one for each
933 `struct driver_info`. The list is in alphabetical order by the name used
934 in `U_BOOT_DRVINFO(name)` and indexed by idx, with the first record having
935 an index of 0. It is only used if OF_PLATDATA_INST is not enabled. This is
936 accessed via macros so that it can be used inside IS_ENABLED(), rather than
937 requiring #ifdefs in the C code when it is not present.
940 This holds a pointer to a list of `struct udevice_rt` records, one for each
941 `struct udevice`. The list is in alphabetical order by the name used
942 in `DM_DEVICE_INST(name)` (a C version of the devicetree node) and indexed by
943 idx, with the first record having an index of 0. It is only used if
944 OF_PLATDATA_INST is enabled. This is accessed via macros so that it can be
945 used inside `IS_ENABLED()`, rather than requiring #ifdefs in the C code when
949 When OF_PLATDATA_RT is enabled, the private/platform data for each device is
950 copied into an allocated region by U-Boot on start-up. This points to that
951 region. All calls to accessor functions (e.g. `dev_get_priv()`) then
952 translate from the pointer provided by the caller (assumed to lie between
953 `__priv_data_start` and `__priv_data_end`) to the new allocated region. This
954 member is accessed via macros so that it can be used inside IS_ENABLED(),
955 rather than required #ifdefs in the C code when it is not present.
957 `struct udevice->flags_`
958 When OF_PLATDATA_RT is enabled, device flags are no-longer part of
959 `struct udevice`, but are instead kept in `struct udevice_rt`, as described
960 above. Flags are accessed via functions, such as `dev_get_flags()` and
963 `struct udevice->node_`
964 When OF_PLATDATA is enabled, there is no devicetree at runtime, so no need
965 for this field. It is removed, just to save space.
968 This macro is used to indicate which phase of U-Boot a driver is intended
969 for. See above for details.
972 This macro is used to indicate which header file dtoc should use to allow
973 a driver declaration to compile correctly. See above for details.
975 `device_get_by_ofplat_idx()`
976 There used to be a function called `device_get_by_driver_info()` which
977 looked up a `struct driver_info` pointer and returned the `struct udevice`
978 that was created from it. It was only available for use with of-platdata.
979 This has been removed in favour of `device_get_by_ofplat_idx()` which uses
980 `idx`, the index of the `struct driver_info` or `struct udevice` in the
981 linker_list. Similarly, the `struct phandle_0_arg` (etc.) structs have been
982 updated to use this index instead of a pointer to `struct driver_info`.
985 This has been removed since we now use indexes to obtain a driver from
986 `struct phandle_0_arg` and the like.
989 The original of-platdata tried to order `U_BOOT_DRVINFO()` in the generated
990 files so as to have parents declared ahead of children. This was convenient
991 as it avoided any special code in U-Boot. With OF_PLATDATA_INST this does
992 not work as the idx value relies on using alphabetical order for everything,
993 so that dtoc and U-Boot's linker_lists agree on the idx value. Devices are
994 then bound in order of idx, having no regard to parent/child relationships.
995 For this reason, device binding now hapens in multiple passes, with parents
996 being bound before their children. This is important so that children can
997 find their parents in the bind() method if needed.
1000 The root device is generally bound by U-Boot but with OF_PLATDATA_INST it
1001 cannot be, since binding needs to be done at build time. So in this case
1002 dtoc sets up a root device using `DM_DEVICE_INST()` in `dt-device.c` and
1003 U-Boot makes use of that. When OF_PLATDATA_INST is not enabled, U-Boot
1004 generally ignores the root node and does not create a `U_BOOT_DRVINFO()`
1005 record for it. This means that the idx numbers used by `struct driver_info`
1006 (when OF_PLATDATA_INST is disabled) and the idx numbers used by
1007 `struct udevice` (when OF_PLATDATA_INST is enabled) differ, since one has a
1008 root node and the other does not. This does not actually matter, since only
1009 one of them is actually used for any particular build, but it is worth
1010 keeping in mind if comparing index values and switching OF_PLATDATA_INST on
1013 `__priv_data_start` and `__priv_data_end`
1014 The private/platform data declared by dtoc is all collected together in
1015 a linker section and these symbols mark the start and end of it. This allows
1016 U-Boot to relocate the area to a new location if needed (with
1020 This function converts a private- or platform-data pointer value generated by
1021 dtoc into one that can be used by U-Boot. It is a NOP unless OF_PLATDATA_RT
1022 is enabled, in which case it translates the address to the relocated
1023 region. See above for more information.
1025 The dm_populate_phandle_data() function that was previous needed has now been
1026 removed, since dtoc can address the drivers directly from dt-plat.c and does
1027 not need to fix up things at runtime.
1029 The pylibfdt Python module is used to access the devicetree.
1035 This is an implementation of an idea by Tom Rini <trini@konsulko.com>.
1040 - Consider programmatically reading binding files instead of devicetree
1042 - Allow IS_ENABLED() to be used in the C code instead of #if
1045 .. Simon Glass <sjg@chromium.org>
1048 .. Updated Independence Day 2016
1049 .. Updated 1st October 2020
1050 .. Updated 5th February 2021