On Fri, Aug 07, 2020 at 12:38:02PM +0300, Pekka Paalanen wrote: > On Fri, 7 Aug 2020 11:07:06 +0200 > 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. > > There could be multiple primary planes *usable* for a specific CRTC but > just one used at a time, right? I'm not sure what you mean here, the crtc->primary link is invariant over the lifetime of a driver load. You can't pick a different one, that's set at driver init before drm_dev_register (and hence before userspace ever sees anything). > > 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. > > Why is that needed? With universal planes, I thought > drmModePlane::possible_crtcs bitmask is trustworthy? Yes it should be. > In the legacy KMS UAPI you can't even pick your primary plane, because > it's implied in drmModeSetCrtc(), right? Yup, I thought this all was so userspace knows which plane is the implied one for legacy ioctls. Which does somewhat matter, since page_flip ioctl has more features than atomic (target frame and async mode). > > 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. > > > > 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 :-) > > I'm not sure I see the bonkers there. Userspace has to guess which primary plane is for which crtc, at least if the possible_crtc mask has more than one bit set. Which can happen. -Daniel > > > Thanks, > pq > > > > > Cheers, Daniel > > > > > > > * drm_plane_type for a more in-depth discussion of these special uapi-relevant > > > * plane types. Special planes are associated with their CRTC by calling > > > * drm_crtc_init_with_planes(). > > > -- > > > 2.28.0 > > > > > > > > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
