On Friday, August 7, 2020 11:07 AM, Daniel Vetter <daniel@xxxxxxxx> wrote: > On Thu, Aug 06, 2020 at 10:33:31AM +0000, Simon Ser wrote: > > Some drivers may expose primary planes compatible with multiple CRTCs. > > Make this clear in the docs: the current wording may be misunderstood as > > "exactly one primary plane per CRTC". > > > > Signed-off-by: Simon Ser <contact@xxxxxxxxxxx> > > Cc: Daniel Vetter <daniel@xxxxxxxx> > > --- > > drivers/gpu/drm/drm_plane.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c > > index b7b90b3a2e38..108a922e8c23 100644 > > --- a/drivers/gpu/drm/drm_plane.c > > +++ b/drivers/gpu/drm/drm_plane.c > > @@ -49,8 +49,8 @@ > > * &struct drm_plane (possibly as part of a larger structure) and registers it > > * with a call to drm_universal_plane_init(). > > * > > - * Cursor and overlay planes are optional. All drivers should provide one > > - * primary plane per CRTC to avoid surprising userspace too much. See enum > > + * Cursor and overlay planes are optional. All drivers should provide at least > > + * one primary plane per CRTC to avoid surprising userspace too much. See enum > > I think that's even more confusing, since this reads like there could be > multiple primary planes for a specific CRTC. That's not the case, there' > only one pointer going from drm_crtc->primary to a drm_plane in the > kernel. > > The problem is that userspace doesn't have a drm_property to read this > pointer, and needs to guess. > > I thought the rule is: > > Nth primary plane (or cursor) is the primary plane for the Nth crtc. > Enumaration with increasing drm kms object ids. > > And I guess we should explain that on some hw any plane (including primary > ones, since that's only a sw construct) can be freely assinged to crtc. Eh, wow. Okay, I didn't expect that. :P What does drm_crtc->primary mean in case a GPU exposes more than one CRTC in the primary planes' possible_crtcs bitfield? Does this pointer change if I assign primary plane 2 to CRTC 1? Is the primary n → CRTC n assignment just a default? Maybe we can just say that at most a single primary plane may be assigned to a CRTC, and that a primary plane may be compatible with multiple CRTCs? > Yes it's probably the most gloriously bonkers uapi we've come up with. > Might be so bad that a libdrm helper to look up the primary plane for a > crtc (or it's cursor plane if it exists) would be in order :-) Well, if user-space can change drm_crtc->primary, I'm not sure this is a good idea. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
