[PATCH v1 07/26] drm/panel: remove get_timings

[Laurent Pinchart]

Hi Maxime,

On Tue, Dec 03, 2019 at 08:46:59AM +0100, Maxime Ripard wrote:
> On Mon, Dec 02, 2019 at 08:32:11PM +0100, Sam Ravnborg wrote:
> > There was no users - so remove it.
> > The callback was implemented in two drivers - deleted.
> >
> > Signed-off-by: Sam Ravnborg <sam at ravnborg.org>
> > Cc: Thierry Reding <thierry.reding at gmail.com>
> > Cc: Laurent Pinchart <Laurent.pinchart at ideasonboard.com>
> > Cc: Sam Ravnborg <sam at ravnborg.org>
> > Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> > Cc: Maxime Ripard <mripard at kernel.org>
> > Cc: David Airlie <airlied at linux.ie>
> > Cc: Daniel Vetter <daniel at ffwll.ch>
> > ---
> >  drivers/gpu/drm/panel/panel-seiko-43wvf1g.c | 18 ------------------
> >  drivers/gpu/drm/panel/panel-simple.c        | 18 ------------------
> >  include/drm/drm_panel.h                     |  9 ---------
> >  3 files changed, 45 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panel/panel-seiko-43wvf1g.c b/drivers/gpu/drm/panel/panel-seiko-43wvf1g.c
> > index b878930b17e4..3bcba64235c4 100644
> > --- a/drivers/gpu/drm/panel/panel-seiko-43wvf1g.c
> > +++ b/drivers/gpu/drm/panel/panel-seiko-43wvf1g.c
> > @@ -217,30 +217,12 @@ static int seiko_panel_get_modes(struct drm_panel *panel,
> >  	return seiko_panel_get_fixed_modes(p, connector);
> >  }
> >
> > -static int seiko_panel_get_timings(struct drm_panel *panel,
> > -				    unsigned int num_timings,
> > -				    struct display_timing *timings)
> > -{
> > -	struct seiko_panel *p = to_seiko_panel(panel);
> > -	unsigned int i;
> > -
> > -	if (p->desc->num_timings < num_timings)
> > -		num_timings = p->desc->num_timings;
> > -
> > -	if (timings)
> > -		for (i = 0; i < num_timings; i++)
> > -			timings[i] = p->desc->timings[i];
> > -
> > -	return p->desc->num_timings;
> > -}
> > -
> >  static const struct drm_panel_funcs seiko_panel_funcs = {
> >  	.disable = seiko_panel_disable,
> >  	.unprepare = seiko_panel_unprepare,
> >  	.prepare = seiko_panel_prepare,
> >  	.enable = seiko_panel_enable,
> >  	.get_modes = seiko_panel_get_modes,
> > -	.get_timings = seiko_panel_get_timings,
> >  };
> 
> If anything, I think we should grow the usage of timings and / or make
> it usable by everyone.
> 
> Using only the mode as we do currently has a bunch of shortcomings as
> almost no encoder will be able to provide the typical pixel clock, and
> that situation leads to multiple things:
> 
>   - If someone working on one encoder wants to upstream a panel they
>     have tested, chances are this will not be the typical pixel clock
>     / timings being used but rather the one that will match what that
>     SoC is capable of. Trouble comes when a second user comes in with
>     a different encoder and different capabilities, and then we have a
>     maintainance fight over which timing is the true timing (with a
>     significant chance that none of them are).
> 
>   - If we can't match the pixel clock, we currently have no easy way
>     to make the usual measures of reducing / growing the porches and
>     blankings areas to match the pixel clock we can provide, since we
>     don't have an easy way to get the tolerance on those timings for a
>     given panel. There's some ad hoc solutions on some drivers (I
>     think vc4 has that?) to ignore the panel and just play around with
>     the timings, but I think this should be generalised.
> 
> Timings solves the first case since we have the operating range now
> and not a single set of timings, and it solves the second since we can
> use that range to take those measures instead of taking a shot in the
> dark.
> 
> I appreciate that it's pretty far from where we are today, but
> removing the get_timings means that all the timings already defined in
> the panel drivers are becoming useless too, and that eventually it
> will get removed.

I agree with you.

-- 
Regards,

Laurent Pinchart