linux-kernel - Re: [PATCH v2 1/2] backlight: pwm_bl: Move the checks for initial power state to a separate function

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Message-ID: <1477661234.3010.49.camel@pengutronix.de>
Date:   Fri, 28 Oct 2016 15:27:14 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     thierry.reding@...il.com, lee.jones@...aro.org,
        tomi.valkeinen@...com, linux-pwm@...r.kernel.org,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] backlight: pwm_bl: Move the checks for initial
 power state to a separate function

Hi Peter,

Am Donnerstag, den 27.10.2016, 13:01 +0300 schrieb Peter Ujfalusi:
> Move the checks to select the initial state for the backlight to a new
> function and document the checks we are doing.
>
> At the same time correct the handling of the case when the GPIO is
> initially configured as input: we need to change the direction of the GPIO
> to output and set the GPIO to low as the pin was not driven when the GPIO
> was configured as input.

I think this part should be a separate patch. At least it is a
significant enough change to warrant a mention in the subject.

And I'm not entirely sure this is better than before. If there happens
to be a pull-up on the GPIO (for whatever reason), we might introduce
flicker again if the GPIO goes from input (high) to output (low), and
back to output (high) again due to FB_BLANK_UNBLANK.

regards
Philipp

> With the separate function it is going to be easier to fix or improve the
> initial power state configuration later and it is easier to read the code.
> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> ---
>  drivers/video/backlight/pwm_bl.c | 54 ++++++++++++++++++++++++++--------------
>  1 file changed, 35 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index 12614006211e..74083d880144 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -192,6 +192,32 @@ static int pwm_backlight_parse_dt(struct device *dev,
>  }
>  #endif
>  
> +static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
> +{
> +	struct device_node *node = pb->dev->of_node;
> +
> +	/* Not booted with device tree or no phandle link to the node */
> +	if (!node || !node->phandle)
> +		return FB_BLANK_UNBLANK;
> +
> +	/*
> +	 * 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 the enable GPIO is disabled, do not enable the backlight */

nitpick: s/if/If/ for consistency.

> +	if (pb->enable_gpio && gpiod_get_value(pb->enable_gpio) == 0)
> +		return FB_BLANK_POWERDOWN;
> +
> +	/* The regulator is disabled, do not enable the backlight */
> +	if (!regulator_is_enabled(pb->power_supply))
> +		return FB_BLANK_POWERDOWN;
> +
> +	return FB_BLANK_UNBLANK;
> +}
> +
>  static int pwm_backlight_probe(struct platform_device *pdev)
>  {
>  	struct platform_pwm_backlight_data *data = dev_get_platdata(&pdev->dev);
> @@ -200,7 +226,6 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  	struct backlight_device *bl;
>  	struct device_node *node = pdev->dev.of_node;
>  	struct pwm_bl_data *pb;
> -	int initial_blank = FB_BLANK_UNBLANK;
>  	struct pwm_args pargs;
>  	int ret;
>  
> @@ -267,20 +292,14 @@ 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 (node && node->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);
> -	}
> +	/*
> +	 * If the GPIO is configured as input, change the direction to output
> +	 * and set the GPIO as low since the line was not driven when it was
> +	 * configured as input.
> +	 */
> +	if (pb->enable_gpio &&
> +	    gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_IN)
> +		gpiod_direction_output_raw(pb->enable_gpio, 0);
>  
>  	pb->power_supply = devm_regulator_get(&pdev->dev, "power");
>  	if (IS_ERR(pb->power_supply)) {
> @@ -288,9 +307,6 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  		goto err_alloc;
>  	}
>  
> -	if (node && node->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 && !node) {
>  		dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
> @@ -347,7 +363,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  	}
>  
>  	bl->props.brightness = data->dft_brightness;
> -	bl->props.power = initial_blank;
> +	bl->props.power = pwm_backlight_initial_power_state(pb);
>  	backlight_update_status(bl);
>  
>  	platform_set_drvdata(pdev, bl);