fsi/fsi-master-gpio: Add "no-gpio-delays" option

This adds support for an optional device-tree property that
makes the driver skip all the delays around clocking the
GPIOs and set it in the device-tree of common POWER9 based
OpenPower platforms.

This useful on chips like the AST2500 where the GPIO block is
running at a fairly low clock frequency (25Mhz typically). In
this case, the delays are unnecessary and due to the low
precision of the timers, actually quite harmful in terms of
performance.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Christopher Bostic <cbostic@linux.vnet.ibm.com>
Tested-by: Joel Stanley <joel@jms.id.au>

diff --git a/arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts b/arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts
index 389f5f8..0b9b37d 100644 (file)
--- a/arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts
+++ b/arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts
@@ -52,6 +52,7 @@
                compatible = "fsi-master-gpio", "fsi-master";
                #address-cells = <2>;
                #size-cells = <0>;
+               no-gpio-delays;
 
                clock-gpios = <&gpio ASPEED_GPIO(AA, 0) GPIO_ACTIVE_HIGH>;
                data-gpios = <&gpio ASPEED_GPIO(AA, 2) GPIO_ACTIVE_HIGH>;

diff --git a/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts b/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts
index 78a511e..6560361 100644 (file)
--- a/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts
+++ b/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts
@@ -153,6 +153,7 @@
                compatible = "fsi-master-gpio", "fsi-master";
                #address-cells = <2>;
                #size-cells = <0>;
+               no-gpio-delays;
 
                clock-gpios = <&gpio ASPEED_GPIO(AA, 0) GPIO_ACTIVE_HIGH>;
                data-gpios = <&gpio ASPEED_GPIO(E, 0) GPIO_ACTIVE_HIGH>;

diff --git a/arch/arm/boot/dts/aspeed-bmc-opp-zaius.dts b/arch/arm/boot/dts/aspeed-bmc-opp-zaius.dts
index ccbf645..2c5aa90 100644 (file)
--- a/arch/arm/boot/dts/aspeed-bmc-opp-zaius.dts
+++ b/arch/arm/boot/dts/aspeed-bmc-opp-zaius.dts
@@ -91,6 +91,7 @@
                compatible = "fsi-master-gpio", "fsi-master";
                #address-cells = <2>;
                #size-cells = <0>;
+               no-gpio-delays;
 
                trans-gpios = <&gpio ASPEED_GPIO(O, 6) GPIO_ACTIVE_HIGH>;
                enable-gpios = <&gpio ASPEED_GPIO(D, 0) GPIO_ACTIVE_HIGH>;

diff --git a/drivers/fsi/fsi-master-gpio.c b/drivers/fsi/fsi-master-gpio.c
index d6508bb..c82bbd3 100644 (file)
--- a/drivers/fsi/fsi-master-gpio.c
+++ b/drivers/fsi/fsi-master-gpio.c
@@ -62,6 +62,7 @@ struct fsi_master_gpio {
        struct gpio_desc        *gpio_enable;   /* FSI enable */
        struct gpio_desc        *gpio_mux;      /* Mux control */
        bool                    external_mode;
+       bool                    no_delays;
 };
 
 #define CREATE_TRACE_POINTS
@@ -79,9 +80,11 @@ static void clock_toggle(struct fsi_master_gpio *master, int count)
        int i;
 
        for (i = 0; i < count; i++) {
-               ndelay(FSI_GPIO_STD_DLY);
+               if (!master->no_delays)
+                       ndelay(FSI_GPIO_STD_DLY);
                gpiod_set_value(master->gpio_clk, 0);
-               ndelay(FSI_GPIO_STD_DLY);
+               if (!master->no_delays)
+                       ndelay(FSI_GPIO_STD_DLY);
                gpiod_set_value(master->gpio_clk, 1);
        }
 }
@@ -90,10 +93,12 @@ static int sda_clock_in(struct fsi_master_gpio *master)
 {
        int in;
 
-       ndelay(FSI_GPIO_STD_DLY);
+       if (!master->no_delays)
+               ndelay(FSI_GPIO_STD_DLY);
        gpiod_set_value(master->gpio_clk, 0);
        in = gpiod_get_value(master->gpio_data);
-       ndelay(FSI_GPIO_STD_DLY);
+       if (!master->no_delays)
+               ndelay(FSI_GPIO_STD_DLY);
        gpiod_set_value(master->gpio_clk, 1);
        return in ? 1 : 0;
 }
@@ -677,6 +682,13 @@ static int fsi_master_gpio_probe(struct platform_device *pdev)
        }
        master->gpio_mux = gpio;
 
+       /*
+        * Check if GPIO block is slow enought that no extra delays
+        * are necessary. This improves performance on ast2500 by
+        * an order of magnitude.
+        */
+       master->no_delays = device_property_present(&pdev->dev, "no-gpio-delays");
+
        master->master.n_links = 1;
        master->master.flags = FSI_MASTER_FLAG_SWCLOCK;
        master->master.read = fsi_master_gpio_read;