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

[Noralf TrÃnnes]

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@xxxxxxxxxxx>
> > +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