[PATCH] backlight: pwm_bl: re-add driver internal enabled tracking

[Daniel Thompson]

On Fri, Nov 09, 2018 at 10:48:57AM +0100, Heiko Stuebner wrote:
> Commit e6bcca0890b9 ("backlight: pwm_bl: Switch to using "atomic" PWM API")
> removed the driver internal enabled tracking in favor of simply checking
> the pwm state.
> 
> This can lead to issues as all of gpio-, regulator- and pwm-state are used
> to determine the initial state and the bootloader or kernel can leave them
> in an inconsistent state at boot.
> 
> In my case on rk3399-kevin, the pwm backlight is build as module and the
> kernel disables the supply regulator as unused while keeping the pwm running
> thus pwm_bl calling pwm_backlight_power_off() during probe and creating an
> unmatched regulator-disable call, as it never got enabled from the pwm-bl
> before.
> 
> To prevent these consistency issues, reintroduce the driver-internal
> tracking of the enabled state.
> 
> Fixes: e6bcca0890b9 ("backlight: pwm_bl: Switch to using "atomic" PWM API")
> Signed-off-by: Heiko Stuebner <heiko at sntech.de>

Acked-by: Daniel Thompson <daniel.thompson at linaro.org>

> ---
>  drivers/video/backlight/pwm_bl.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index 678b27063198..bcd08b41765d 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -30,6 +30,7 @@ struct pwm_bl_data {
>  	struct device		*dev;
>  	unsigned int		lth_brightness;
>  	unsigned int		*levels;
> +	bool			enabled;
>  	struct regulator	*power_supply;
>  	struct gpio_desc	*enable_gpio;
>  	unsigned int		scale;
> @@ -50,7 +51,7 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb)
>  	int err;
>  
>  	pwm_get_state(pb->pwm, &state);
> -	if (state.enabled)
> +	if (pb->enabled)
>  		return;
>  
>  	err = regulator_enable(pb->power_supply);
> @@ -65,6 +66,8 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb)
>  
>  	if (pb->enable_gpio)
>  		gpiod_set_value_cansleep(pb->enable_gpio, 1);
> +
> +	pb->enabled = true;
>  }
>  
>  static void pwm_backlight_power_off(struct pwm_bl_data *pb)
> @@ -72,7 +75,7 @@ static void pwm_backlight_power_off(struct pwm_bl_data *pb)
>  	struct pwm_state state;
>  
>  	pwm_get_state(pb->pwm, &state);
> -	if (!state.enabled)
> +	if (!pb->enabled)
>  		return;
>  
>  	if (pb->enable_gpio)
> @@ -86,6 +89,7 @@ static void pwm_backlight_power_off(struct pwm_bl_data *pb)
>  	pwm_apply_state(pb->pwm, &state);
>  
>  	regulator_disable(pb->power_supply);
> +	pb->enabled = false;
>  }
>  
>  static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness)
> @@ -483,6 +487,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  	pb->check_fb = data->check_fb;
>  	pb->exit = data->exit;
>  	pb->dev = &pdev->dev;
> +	pb->enabled = false;
>  	pb->post_pwm_on_delay = data->post_pwm_on_delay;
>  	pb->pwm_off_delay = data->pwm_off_delay;
>  
> -- 
> 2.18.0
>