drm/amdgpu: Fixes to the AMDGPU EEPROM driver

* When reading from the EEPROM device, there is no
  device limitation on the number of bytes
  read--they're simply sequenced out. Thus, read
  the whole data requested in one go.

* When writing to the EEPROM device, there is a
  256-byte page limit to write to before having to
  generate a STOP on the bus, as well as the
  address written to mustn't cross over the page
  boundary (it actually rolls over). Maximize the
  data written to per bus acquisition.

* Return the number of bytes read/written, or -errno.

* Add kernel doc.

Cc: Jean Delvare <jdelvare@suse.de>
Cc: Alexander Deucher <Alexander.Deucher@amd.com>
Cc: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Cc: Lijo Lazar <Lijo.Lazar@amd.com>
Cc: Stanley Yang <Stanley.Yang@amd.com>
Cc: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Acked-by: Alexander Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
index d02ea08..7fdb5bd 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
@@ -24,59 +24,99 @@
 #include "amdgpu_eeprom.h"
 #include "amdgpu.h"
 
-#define EEPROM_OFFSET_LENGTH 2
+/* AT24CM02 has a 256-byte write page size.
+ */
+#define EEPROM_PAGE_BITS   8
+#define EEPROM_PAGE_SIZE   (1U << EEPROM_PAGE_BITS)
+#define EEPROM_PAGE_MASK   (EEPROM_PAGE_SIZE - 1)
+
+#define EEPROM_OFFSET_SIZE 2
 
+/**
+ * amdgpu_eeprom_xfer -- Read/write from/to an I2C EEPROM device
+ * @i2c_adap: pointer to the I2C adapter to use
+ * @slave_addr: I2C address of the slave device
+ * @eeprom_addr: EEPROM address from which to read/write
+ * @eeprom_buf: pointer to data buffer to read into/write from
+ * @buf_size: the size of @eeprom_buf
+ * @read: True if reading from the EEPROM, false if writing
+ *
+ * Returns the number of bytes read/written; -errno on error.
+ */
 int amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
                       u16 slave_addr, u16 eeprom_addr,
-                      u8 *eeprom_buf, u16 bytes, bool read)
+                      u8 *eeprom_buf, u16 buf_size, bool read)
 {
-       u8 eeprom_offset_buf[2];
-       u16 bytes_transferred;
+       u8 eeprom_offset_buf[EEPROM_OFFSET_SIZE];
        struct i2c_msg msgs[] = {
                {
                        .addr = slave_addr,
                        .flags = 0,
-                       .len = EEPROM_OFFSET_LENGTH,
+                       .len = EEPROM_OFFSET_SIZE,
                        .buf = eeprom_offset_buf,
                },
                {
                        .addr = slave_addr,
                        .flags = read ? I2C_M_RD : 0,
-                       .len = bytes,
-                       .buf = eeprom_buf,
                },
        };
+       const u8 *p = eeprom_buf;
        int r;
+       u16 len;
+
+       r = 0;
+       for (len = 0; buf_size > 0;
+            buf_size -= len, eeprom_addr += len, eeprom_buf += len) {
+               /* Set the EEPROM address we want to write to/read from.
+                */
+               msgs[0].buf[0] = (eeprom_addr >> 8) & 0xff;
+               msgs[0].buf[1] = eeprom_addr & 0xff;
 
-       msgs[0].buf[0] = ((eeprom_addr >> 8) & 0xff);
-       msgs[0].buf[1] = (eeprom_addr & 0xff);
+               if (!read) {
+                       /* Write the maximum amount of data, without
+                        * crossing the device's page boundary, as per
+                        * its spec. Partial page writes are allowed,
+                        * starting at any location within the page,
+                        * so long as the page boundary isn't crossed
+                        * over (actually the page pointer rolls
+                        * over).
+                        *
+                        * As per the AT24CM02 EEPROM spec, after
+                        * writing into a page, the I2C driver MUST
+                        * terminate the transfer, i.e. in
+                        * "i2c_transfer()" below, with a STOP
+                        * condition, so that the self-timed write
+                        * cycle begins. This is implied for the
+                        * "i2c_transfer()" abstraction.
+                        */
+                       len = min(EEPROM_PAGE_SIZE - (eeprom_addr &
+                                                     EEPROM_PAGE_MASK),
+                                 (u32)buf_size);
+               } else {
+                       /* Reading from the EEPROM has no limitation
+                        * on the number of bytes read from the EEPROM
+                        * device--they are simply sequenced out.
+                        */
+                       len = buf_size;
+               }
+               msgs[1].len = len;
+               msgs[1].buf = eeprom_buf;
 
-       while (msgs[1].len) {
                r = i2c_transfer(i2c_adap, msgs, ARRAY_SIZE(msgs));
-               if (r <= 0)
-                       return r;
+               if (r < ARRAY_SIZE(msgs))
+                       break;
 
-               /* Only for write data */
-               if (!msgs[1].flags)
-                       /*
-                        * According to EEPROM spec there is a MAX of 10 ms required for
-                        * EEPROM to flush internal RX buffer after STOP was issued at the
-                        * end of write transaction. During this time the EEPROM will not be
-                        * responsive to any more commands - so wait a bit more.
+               if (!read) {
+                       /* According to the AT24CM02 EEPROM spec the
+                        * length of the self-writing cycle, tWR, is
+                        * 10 ms.
                         *
                         * TODO Improve to wait for first ACK for slave address after
                         * internal write cycle done.
                         */
                        msleep(10);
-
-
-               bytes_transferred = r - EEPROM_OFFSET_LENGTH;
-               eeprom_addr += bytes_transferred;
-               msgs[0].buf[0] = ((eeprom_addr >> 8) & 0xff);
-               msgs[0].buf[1] = (eeprom_addr & 0xff);
-               msgs[1].buf += bytes_transferred;
-               msgs[1].len -= bytes_transferred;
+               }
        }
 
-       return 0;
+       return r < 0 ? r : eeprom_buf - p;
 }