Hi,

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@ravnborg.org>
> Cc: Thierry Reding <thierry.reding@gmail.com>
> Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Daniel Vetter <daniel@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.

Maxime