linux-kernel - Re: [PATCH 3/4] drm: Add helper for simple display pipeline

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Message-ID: <8b885635-4df5-e902-a755-3f32cab75131@tronnes.org>
Date:	Mon, 9 May 2016 20:37:39 +0200
From:	Noralf Trønnes <noralf@...nnes.org>
To:	Daniel Vetter <daniel@...ll.ch>
Cc:	dri-devel@...ts.freedesktop.org, treding@...dia.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] drm: Add helper for simple display pipeline


Den 09.05.2016 16:46, skrev Daniel Vetter:
> On Thu, May 05, 2016 at 03:24:33PM +0200, Noralf Trønnes wrote:
>> Provides helper functions for drivers that have a simple display
>> pipeline. Plane, crtc and encoder are collapsed into one entity.
>>
>> Signed-off-by: Noralf Trønnes <noralf@...nnes.org>
>> +static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane,
>> +					struct drm_plane_state *pstate)
>> +{
>> +	struct drm_simple_display_pipe *pipe;
>> +	struct drm_crtc_state *cstate;
>> +
>> +	pipe = container_of(plane, struct drm_simple_display_pipe, plane);
>> +	if (!pipe->funcs || !pipe->funcs->check)
>> +		return 0;
>> +
>> +	cstate = drm_atomic_get_existing_crtc_state(pstate->state,
>> +						    &pipe->crtc);
>> +
>> +	return pipe->funcs->check(pipe, pstate, cstate);
>> +}
> Ok one thing I've missed here is that for most drivers this is way too
> simple a check function, which means we'll end up with tons of duplicated
> code. Things which the drm core allows, but simple pipelines all don't
> really cope with:
> - plane scaling
> - disabling the plane without the crtc (i.e. scan out black)
> - plane not sized to fill the entire hactive/vactive
>
> There's a helper to do most of these checks for you -
> drm_plane_helper_check_update. I think it'd be good to place a call for
> that in here, before we call down into the driver's ->check callback. But
> ofc before we return 0; we want these checks always done. And catch all
> these things so that drivers never fall over this pitfall.

Does this resemble what you're after? I'm just guessing here.

static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane,
                     struct drm_plane_state *pstate)
{
     struct drm_rect src = {
         .x1 = pstate->src_x,
         .y1 = pstate->src_y,
         .x2 = pstate->src_x + pstate->src_w,
         .y2 = pstate->src_y + pstate->src_h,
     };
     struct drm_rect dest = {
         .x1 = pstate->crtc_x,
         .y1 = pstate->crtc_y,
         .x2 = pstate->crtc_x + pstate->crtc_w,
         .y2 = pstate->crtc_y + pstate->crtc_h,
     };
     struct drm_rect clip = { 0 };
     struct drm_simple_display_pipe *pipe;
     struct drm_crtc_state *cstate;
     bool visible;
     int ret;

     pipe = container_of(plane, struct drm_simple_display_pipe, plane);
     clip.x2 = pipe->crtc.mode.hdisplay;
     clip.y2 = pipe->crtc.mode.vdisplay;
     ret = drm_plane_helper_check_update(plane, &pipe->crtc, plane->fb,
                         &src, &dest, &clip,
                         DRM_PLANE_HELPER_NO_SCALING,
                         DRM_PLANE_HELPER_NO_SCALING,
                         false, false, &visible);
     if (ret)
         return ret;

     /* How to handle !visible, is it even possible? */

     if (!pipe->funcs || !pipe->funcs->check)
         return 0;

     cstate = drm_atomic_get_existing_crtc_state(pstate->state,
                             &pipe->crtc);

     return pipe->funcs->check(pipe, pstate, cstate);
}


Noralf.

> Noticed while discussing tilcdc atomic patches, since tilcdc could
> probably use drm_simple_display_pipe too.
> -Daniel