Hi,
On Fri, 2019-05-17 at 17:05 +0200, Paul Kocialkowski wrote:
> On a trivial gpio-backlight setup with a panel using the backlight but
> no boot software to enable it beforehand, we fall in a case where the
> backlight is disabled (not just blanked) and thus remains disabled when
> the panel gets enabled.
>
> Setting gbl->def_value via the device-tree prop allows enabling the
> backlight in this situation, but it will be unblanked straight away,
> in compliance with the binding. This does not work well when there was no
> boot software to display something before, since we really need to unblank
> by the time the panel is enabled, not before.
>
> Resolve the situation by setting the brightness to 1 at probe and
> managing the power state accordingly, a bit like it's done in
> pwm-backlight.
Any feedback on this? I was under the impression that it could be quite
controversial, as it implies that the backlight can no longer be
enabled without a bound panel (which IMO makes good sense but could be
a matter to debate).
Cheers,
Paul
> Fixes: 8b770e3c9824 ("backlight: Add GPIO-based backlight driver")
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx>
> ---
> drivers/video/backlight/gpio_backlight.c | 19 ++++++++++++++++++-
> 1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c
> index e470da95d806..c9cb97fa13d0 100644
> --- a/drivers/video/backlight/gpio_backlight.c
> +++ b/drivers/video/backlight/gpio_backlight.c
> @@ -57,6 +57,21 @@ static const struct backlight_ops gpio_backlight_ops = {
> .check_fb = gpio_backlight_check_fb,
> };
>
> +static int gpio_backlight_initial_power_state(struct gpio_backlight *gbl)
> +{
> + struct device_node *node = gbl->dev->of_node;
> +
> + /* If we absolutely want the backlight enabled at boot. */
> + if (gbl->def_value)
> + return FB_BLANK_UNBLANK;
> +
> + /* If there's no panel to unblank the backlight later. */
> + if (!node || !node->phandle)
> + return FB_BLANK_UNBLANK;
> +
> + return FB_BLANK_POWERDOWN;
> +}
> +
> static int gpio_backlight_probe_dt(struct platform_device *pdev,
> struct gpio_backlight *gbl)
> {
> @@ -142,7 +157,9 @@ static int gpio_backlight_probe(struct platform_device *pdev)
> return PTR_ERR(bl);
> }
>
> - bl->props.brightness = gbl->def_value;
> + bl->props.brightness = 1;
> + bl->props.power = gpio_backlight_initial_power_state(gbl);
> +
> backlight_update_status(bl);
>
> platform_set_drvdata(pdev, bl);
--
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com
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