lkml.org 
[lkml]   [2019]   [Aug]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [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@ti.com>

Reviewed-by: Daniel Thompson <daniel.thompson@linaro.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.
> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

\
 
 \ /
  Last update: 2019-08-21 16:05    [W:0.093 / U:0.832 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site