Re: [PATCH v1 2/3] drm/panel: update backlight handling for samsung-s6e63j0x03

[Sam Ravnborg <sam@ravnborg.org>]

Hi Emil.

Thanks for your feedback!

On Thu, Apr 09, 2020 at 03:13:28PM +0100, Emil Velikov wrote:
> On Thu, 9 Apr 2020 at 12:53, Sam Ravnborg <sam@ravnborg.org> wrote:
> >
> > The samsung-s6e63j0x03 had a local way to handle backlight.
> >
> > Update the driver to use a devm_ based register function
> > and utilize drm_panel backlight support. The changes results
> > in a simpler driver with the same functionality.
> >
> > Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
> > Cc: Joonas Kylmälä <joonas.kylmala@iki.fi>
> > Cc: Andrzej Hajda <a.hajda@samsung.com>
> > Cc: Thierry Reding <thierry.reding@gmail.com>
> > Cc: Inki Dae <inki.dae@samsung.com>
> > Cc: Hyungwon Hwang <human.hwang@samsung.com>
> > Cc: Hoegeun Kwon <hoegeun.kwon@samsung.com>
> > ---
> >  .../gpu/drm/panel/panel-samsung-s6e63j0x03.c  | 55 ++++++++++---------
> >  1 file changed, 29 insertions(+), 26 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panel/panel-samsung-s6e63j0x03.c b/drivers/gpu/drm/panel/panel-samsung-s6e63j0x03.c
> > index a3570e0a90a8..2c035f87e3f0 100644
> > --- a/drivers/gpu/drm/panel/panel-samsung-s6e63j0x03.c
> > +++ b/drivers/gpu/drm/panel/panel-samsung-s6e63j0x03.c
> > @@ -36,7 +36,6 @@
> >  struct s6e63j0x03 {
> >         struct device *dev;
> >         struct drm_panel panel;
> > -       struct backlight_device *bl_dev;
> >
> >         struct regulator_bulk_data supplies[2];
> >         struct gpio_desc *reset_gpio;
> > @@ -184,7 +183,7 @@ static unsigned int s6e63j0x03_get_brightness_index(unsigned int brightness)
> >  static int s6e63j0x03_update_gamma(struct s6e63j0x03 *ctx,
> >                                         unsigned int brightness)
> >  {
> > -       struct backlight_device *bl_dev = ctx->bl_dev;
> > +       struct backlight_device *bl_dev = ctx->panel.backlight;
> >         unsigned int index = s6e63j0x03_get_brightness_index(brightness);
> >         int ret;
> >
> > @@ -217,6 +216,30 @@ static const struct backlight_ops s6e63j0x03_bl_ops = {
> >         .update_status = s6e63j0x03_set_brightness,
> >  };
> >
> > +static int s6e63j0x03_backlight_register(struct s6e63j0x03 *ctx)
> > +{
> > +       struct backlight_properties props = {
> Pretty sure we can (should really) make the props const.
Thanks, will fix either in v2 or when I apply.

> 
> Quick grep through drm, shows that there're other offenders, so might
> as well do that in separate series.
> Seems like other panels could follow suite, with later series of course.
> 
> Back on topic, it's not immediately obvious why the FB_BLANK_*
> handling is safe to remove. Please add small mention in the commit log
> mentioning why.

Maybe because it is not so?
Lets take a closer look.
backlight_enable() and backlight_disable() are called from
drm_panel - because drm_panel->backlight is assigned.


drm_panel_prepare:
OLD:	ctx->bl_dev->props.power = FB_BLANK_NORMAL;
NEW:

drm_panel_enable:
OLD:	ctx->bl_dev->props.power = FB_BLANK_UNBLANK;
NEW:	backlight_enable() => 
		bd->props.power = FB_BLANK_UNBLANK;
		bd->props.fb_blank = FB_BLANK_UNBLANK;
	        bd->props.state &= ~BL_CORE_FBBLANK;

drm_panel_disable:
OLD:	ctx->bl_dev->props.power = FB_BLANK_NORMAL;
NEW:	backlight_disable() =>
		bd->props.power = FB_BLANK_POWERDOWN;
	        bd->props.fb_blank = FB_BLANK_POWERDOWN;
        	bd->props.state |= BL_CORE_FBBLANK;


drm_panel_unprepare:
OLD:	ctx->bl_dev->props.power = FB_BLANK_POWERDOWN;
NEW:

So old and new code are not exactly the same.

But with my (limited) backlight understanding this should
work as expected - and it works for many other drivers.
So if this does not work, then we should look at the backlight
handling and not do workarounds in the driver.

I will summarize the above in the individual changelogs.

	Sam


> 
> -Emil
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