[PATCH v5] pwm-backlight: Avoid backlight flicker when probed from DT

Lee Jones
2015-11-24T16:26:58Z

On Wed, 18 Nov 2015, Philipp Zabel wrote:

> If the driver is probed from the device tree, and there is a phandle
> property set on it, and the enable GPIO is already configured as output,
> and the backlight is currently disabled, keep it disabled.
> If all these conditions are met, assume there will be some other driver
> that can enable the backlight at the appropriate time.
>
> Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
> Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
> Tested-by: Heiko Stuebner <heiko@sntech.de>
> ---
> - Rebased onto v4.4-rc1
> - Added Heiko's Tested-by
> ---
> drivers/video/backlight/pwm_bl.c | 23 ++++++++++++++++++++++-
> 1 file changed, 22 insertions(+), 1 deletion(-)

Applied, thanks.

> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index ae3c6b6..3daf9cc 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -199,6 +199,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> struct backlight_properties props;
> struct backlight_device *bl;
> struct pwm_bl_data *pb;
> + phandle phandle = pdev->dev.of_node->phandle;
> + int initial_blank = FB_BLANK_UNBLANK;
> int ret;
>
> if (!data) {
> @@ -242,7 +244,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> pb->enabled = false;
>
> pb->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
> - GPIOD_OUT_HIGH);
> + GPIOD_ASIS);
> if (IS_ERR(pb->enable_gpio)) {
> ret = PTR_ERR(pb->enable_gpio);
> goto err_alloc;
> @@ -264,12 +266,30 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> pb->enable_gpio = gpio_to_desc(data->enable_gpio);
> }
>
> + if (pb->enable_gpio) {
> + /*
> + * If the driver is probed from the device tree and there is a
> + * phandle link pointing to the backlight node, it is safe to
> + * assume that another driver will enable the backlight at the
> + * appropriate time. Therefore, if it is disabled, keep it so.
> + */
> + if (phandle &&
> + gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_OUT &&
> + gpiod_get_value(pb->enable_gpio) == 0)
> + initial_blank = FB_BLANK_POWERDOWN;
> + else
> + gpiod_direction_output(pb->enable_gpio, 1);
> + }
> +
> pb->power_supply = devm_regulator_get(&pdev->dev, "power");
> if (IS_ERR(pb->power_supply)) {
> ret = PTR_ERR(pb->power_supply);
> goto err_alloc;
> }
>
> + if (phandle && !regulator_is_enabled(pb->power_supply))
> + initial_blank = FB_BLANK_POWERDOWN;
> +
> pb->pwm = devm_pwm_get(&pdev->dev, NULL);
> if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER
> && !pdev->dev.of_node) {
> @@ -320,6 +340,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> }
>
> bl->props.brightness = data->dft_brightness;
> + bl->props.power = initial_blank;
> backlight_update_status(bl);
>
> platform_set_drvdata(pdev, bl);

--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org ? Open source software for ARM SoCs
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