[PATCH] drm/atomic: refuse changing CRTC for planes directly

[Ville Syrjälä]

On Wed, Aug 26, 2015 at 12:07:30PM -0400, Rob Clark wrote:
> On Wed, Aug 26, 2015 at 12:03 PM, Rob Clark <robdclark at gmail.com> wrote:
> > On Wed, Aug 26, 2015 at 11:41 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> >> Very strictly speaking this is possible if you have special hw and
> >> genlocked CRTCs. In general switching a plane between two active CRTC
> >> just won't work so well and is probably not tested at all. Just forbid
> >> it.
> >
> > So, I expect msm should actually be able to do this w/ dual-dsi (where
> > we are using two CRTC's, w/ synchronized flushes)..
> >
> > Probably someone who has a dual-dsi panel should actually test that to
> > confirm.  But it seems like it should work.  Maybe we need something
> > in 'struct drm_crtc' so core can realize that two CRTC's are locked
> > together..
> 
> oh, and for most drivers, switching plane between CRTCs without an
> off-cycle would probably also work for DSI cmd mode..

You'd need to wait for any ongoing transfer on the old crtc to finish
before moving the plane. So that's not really any different than the
driver doing the dance with a vblank wait on a video mode display.

> 
> BR,
> -R
> 
> >
> >> I've put this into the core since I really couldn't come up with a
> >> case where we don't want to enforce that. But if that ever happens it
> >> would be easy to move this check into helpers.
> >>
> >> v2: don't bother with complexity and just outright disallow plane
> >> switching without the intermediate OFF state. Simplifies drivers, we
> >> don't have any hw that could do it anyway and current atomic userspace
> >> (weston) works like this already anyway.
> >>
> >> Cc: Thierry Reding <thierry.reding at gmail.com>
> >> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> >> Cc: Daniel Stone <daniels at collabora.com>
> >> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> >> ---
> >>  drivers/gpu/drm/drm_atomic.c | 22 ++++++++++++++++++++++
> >>  1 file changed, 22 insertions(+)
> >>
> >> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> >> index 434915448ea0..f27aae3fa765 100644
> >> --- a/drivers/gpu/drm/drm_atomic.c
> >> +++ b/drivers/gpu/drm/drm_atomic.c
> >> @@ -663,6 +663,22 @@ drm_atomic_plane_get_property(struct drm_plane *plane,
> >>         return 0;
> >>  }
> >>
> >> +static bool
> >> +plane_switching(struct drm_atomic_state *state,
> >> +               struct drm_plane *plane,
> >> +               struct drm_plane_state *plane_state)
> >> +{
> >> +       struct drm_crtc_state *crtc_state, *curr_crtc_state;
> >> +
> >> +       if (!plane->state->crtc || !plane_state->crtc)
> >> +               return false;
> >> +
> >> +       if (plane->state->crtc == plane_state->crtc)
> >> +               return false;
> >> +
> >> +       return true;
> >> +}
> >> +
> >>  /**
> >>   * drm_atomic_plane_check - check plane state
> >>   * @plane: plane to check
> >> @@ -734,6 +750,12 @@ static int drm_atomic_plane_check(struct drm_plane *plane,
> >>                 return -ENOSPC;
> >>         }
> >>
> >> +       if (plane_switching(state->state, plane, state)) {
> >> +               DRM_DEBUG_ATOMIC("[PLANE:%d] switching CRTC directly\n",
> >> +                                plane->base.id);
> >> +               return -EINVAL;
> >> +       }
> >> +
> >>         return 0;
> >>  }
> >>
> >> --
> >> 2.5.0
> >>
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> >> http://lists.freedesktop.org/mailman/listinfo/dri-devel
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-- 
Ville Syrjälä
Intel OTC