On Tue, 2018-05-29 at 11:30 +1000, Benjamin Herrenschmidt wrote:
> 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.
Forgot to add the DT binding documentation, I'll send it as a separate
patch.
> Signed-off-by: Benjamin Herrenschmidt <b...@kernel.crashing.org>
> Reviewed-by: Christopher Bostic <cbos...@linux.vnet.ibm.com>
> ---
> arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts | 1 +
> .../boot/dts/aspeed-bmc-opp-witherspoon.dts | 1 +
> arch/arm/boot/dts/aspeed-bmc-opp-zaius.dts | 1 +
> drivers/fsi/fsi-master-gpio.c | 20 +++++++++++++++----
> 4 files changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts
> b/arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts
> index 3a93ae77cde3..71cb9317d624 100644
> --- a/arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts
> +++ b/arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts
> @@ -53,6 +53,7 @@
> 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 dab467463c99..97cf819309b5 100644
> --- a/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts
> +++ b/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts
> @@ -126,6 +126,7 @@
> 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 f3bc89a4262f..71a64730f080 100644
> --- a/arch/arm/boot/dts/aspeed-bmc-opp-zaius.dts
> +++ b/arch/arm/boot/dts/aspeed-bmc-opp-zaius.dts
> @@ -86,6 +86,7 @@
> 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 d6508bbad1fb..c82bbd35276e 100644
> --- 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;
