On Thu, Nov 01, 2012 at 07:39:12AM -0700, Jesse Barnes wrote:
On Thu, 1 Nov 2012 12:12:35 +0100 Daniel Vetter daniel@ffwll.ch wrote:
On Thu, Oct 25, 2012 at 8:05 PM, ville.syrjala@linux.intel.com wrote:
From: Ville Syrjälä ville.syrjala@linux.intel.com
Send completion events when the atomic modesetting operations has finished succesfully.
Signed-off-by: Ville Syrjälä ville.syrjala@linux.intel.com
I have to admit I'm not on top of the latest ioctl/interface discussion, but one new requirement for the modeset (not the pageflip part) of the all this atomic stuff I've discovered is that the kernel needs to be able to select the crtcs for each output completely unrestricted. I think userspace should simply pass in abstract crtc ids (e.g. 0, 1, 2, ...) and the kernel then passes back the actual crtcs it has selected.
We can't do that remapping internally because the crtc abstraction is leaky:
- wait_for_vblank requires the pipe id, which could then change on every modeset
- similarly userspace doing MI_WAIT for scanlines needs to know the
actual hw pipe in use by a crtc. And current userspace presumes that the mapping between crtc->pipe doesn't change.
An example why the kernel needs to pick the crtc for userspace:
- on ivb only pipe A has a 7x5 panel fitter, so usually you want to
put the panel on the first crtc
- but if you run in a 3 pipe configuration and have an eDP panel, it's
better to put the eDP output on pipe C, since then pipes A&B will have full 4-lane fdi links to the pch ports (instead of otherwise only 2 lanes each on links B&C)
- similarly when we have a 3 pipe configuration with all encoders on
the pch, we need to move the mode with the highest dotclock to pipe A (since that's the only one which will have 4 lanes, pipe B&C will only have 2 each).
- afaik these kind of asymmetric constraints won't disappear anytime
soon, haswell definitely still has some.
Yeah that's a good point... adding a virtual crtc layer would solve this and let us preserve the existing ABI.
How would the state handling work? I mean if drm_crtc X currently has some state, drm_crtc Y has some other state, and then we do a modeset which would require swapping the roles of the crtcs, what would happen to the bits of state that we didn't specify?
If we'd do the remapping below the drm crtc layer, the state would always be tied to the drm crtc. But that would definitely require mostly uniform hardware "crtcs" so that the capabilities of the drm_crtcs wouldn't keep changing whenever the remap happens.
Well, I suppose we could tie the state to the virtual crtc instead, and doing an operation on a real drm_crtc would also change the state of the currently bound virtual crtc. And then changing the virtual<->real mapping would just copy the state over from the virtual crtc to the real drm_crtc.
And if we do it for crtcs, then we'd need to do it for planes as well, because the plane<->crtc mapping can be fixed or otherwise limited in some fashion.
Either way it sounds rather messy to me.
Another option would be just leave it up to userspace to make the correct choice between crtcs and planes. But then user space needs to be equipped with more hardware specific knowledge, so it's not a very appealing idea either.