[PATCH linux dev-4.13 4/6] fsi/fsi-master-gpio: Add "no-gpio-delays" option

[Christopher Bostic]

Reviewed-by: Christopher Bostic <cbostic at linux.vnet.ibm.com>


On 5/7/18 8:06 PM, 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.
>
> Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> ---
>   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 d746e562e8fd..0fdf08077ed3 100644
> --- a/arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts
> +++ b/arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts
> @@ -59,6 +59,7 @@
>   		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 596608f4b936..214718b7784d 100644
> --- a/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts
> +++ b/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts
> @@ -160,6 +160,7 @@
>   		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 7f5a29566801..085926935574 100644
> --- 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 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;