linux-kernel - Re: [PATCH v3] backlight: gpio-backlight: Correct initial power state handling

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Message-ID: <20190821140454.6uuquwx7bkyx656e@holly.lan>
Date:   Wed, 21 Aug 2019 15:04:54 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     lee.jones@...aro.org, jingoohan1@...il.com,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, paul.kocialkowski@...tlin.com
Subject: Re: [PATCH v3] backlight: gpio-backlight: Correct initial power
 state handling

On Wed, Jul 31, 2019 at 11:40:18AM +0300, Peter Ujfalusi wrote:
> The default-on property - or the def_value via legacy pdata) should be
> handled as:
> if it is 1, the backlight must be enabled (kept enabled)
> if it is 0, the backlight must be disabled (kept disabled)
> 
> This only works for the case when default-on is set. If it is not set then
> the brightness of the backlight is set to 0. Now if the backlight is
> enabled by external driver (graphics) the backlight will stay disabled since
> the brightness is configured as 0. The backlight will not turn on.
> 
> In order to minimize screen flickering during device boot:
> 
> The initial brightness should be set to 1.
> 
> If booted in non DT mode or no phandle link to the backlight node:
> follow the def_value/default-on to select UNBLANK or POWERDOWN
> 
> If in DT boot we have phandle link then leave the GPIO in a state which the
> bootloader left it and let the user of the backlight to configure it
> further.
> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>

Reviewed-by: Daniel Thompson <daniel.thompson@...aro.org>


> ---
> Hi,
> 
> sorry for the delay, but got distracted a bit with the resend of this...
> Let's try again ;)
> 
> Changes since v2 (https://lore.kernel.org/patchwork/patch/1002359/):
> - Rebased on drm-next
> 
> Changes since v1:
> - Implement similiar initial power state handling as pwm backlight have
> 
> Regards,
> Peter
> 
>  drivers/video/backlight/gpio_backlight.c | 24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c
> index e84f3087e29f..18e053e4716c 100644
> --- a/drivers/video/backlight/gpio_backlight.c
> +++ b/drivers/video/backlight/gpio_backlight.c
> @@ -59,13 +59,11 @@ static int gpio_backlight_probe_dt(struct platform_device *pdev,
>  				   struct gpio_backlight *gbl)
>  {
>  	struct device *dev = &pdev->dev;
> -	enum gpiod_flags flags;
>  	int ret;
>  
>  	gbl->def_value = device_property_read_bool(dev, "default-on");
> -	flags = gbl->def_value ? GPIOD_OUT_HIGH : GPIOD_OUT_LOW;
>  
> -	gbl->gpiod = devm_gpiod_get(dev, NULL, flags);
> +	gbl->gpiod = devm_gpiod_get(dev, NULL, GPIOD_ASIS);
>  	if (IS_ERR(gbl->gpiod)) {
>  		ret = PTR_ERR(gbl->gpiod);
>  
> @@ -79,6 +77,22 @@ static int gpio_backlight_probe_dt(struct platform_device *pdev,
>  	return 0;
>  }
>  
> +static int gpio_backlight_initial_power_state(struct gpio_backlight *gbl)
> +{
> +	struct device_node *node = gbl->dev->of_node;
> +
> +	/* Not booted with device tree or no phandle link to the node */
> +	if (!node || !node->phandle)
> +		return gbl->def_value ? FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN;
> +
> +	/* if the enable GPIO is disabled, do not enable the backlight */
> +	if (gpiod_get_value_cansleep(gbl->gpiod) == 0)
> +		return FB_BLANK_POWERDOWN;
> +
> +	return FB_BLANK_UNBLANK;
> +}
> +
> +
>  static int gpio_backlight_probe(struct platform_device *pdev)
>  {
>  	struct gpio_backlight_platform_data *pdata =
> @@ -136,7 +150,9 @@ static int gpio_backlight_probe(struct platform_device *pdev)
>  		return PTR_ERR(bl);
>  	}
>  
> -	bl->props.brightness = gbl->def_value;
> +	bl->props.power = gpio_backlight_initial_power_state(gbl);
> +	bl->props.brightness = 1;
> +
>  	backlight_update_status(bl);
>  
>  	platform_set_drvdata(pdev, bl);
> -- 
> Peter
> 
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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