Re: [PATCH] drm/atomic: pass old crtc state to atomic_begin/flush.

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 15-06-15 om 11:13 schreef Daniel Vetter:
> On Mon, Jun 15, 2015 at 09:30:19AM +0200, Maarten Lankhorst wrote:
>> Op 15-06-15 om 09:10 schreef Daniel Vetter:
>>> On Fri, Jun 12, 2015 at 11:18:22AM +0200, Maarten Lankhorst wrote:
>>>> In intel it's useful to keep track of some state changes with old
>>>> crtc state vs new state, for example to disable initial planes or
>>>> when a modeset's prevented during fastboot.
>>>>
>>>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>>> Hm, thus far the approach has been that the various ->check callbacks diff
>>> the state and set appropriate stuff like needs_modeset or planes_changed.
>>> And with intel_crtc->atomic we've kinda started to build up similar
>>> things for i915. What do you plan to use this for?
>>> -Daniel
>> On a modeset I want to disable all old planes by calling plane->disable_plane, which is old_crtc_state->plane_mask.
>> This is for initial hw readout, where a plane might be active without a fb set. I want to run it during vblank evasion if possible, which
>> means in atomic_begin or flush.
>>
>> commit_plane is not called if the old and new state both have a NULL fb, so the initial plane would stay active in this case.
> Hm, so this is for the i915 state readout code. Imo we shouldn't ever leak
> this out of the state readout code but instead sanitize the plane state to
> make sense. Roughly this would be:
> - read out crtc state
> - try to reconstruct initial fb for primary plane, if this succeeds then
>   fully link up the plane with the crtc in the plane_state.
Agreed. Right now get_initial_plane_config takes an initial_plane_state, could we make this atomic too?

> - then walk all planes for the crtc, and if any plane is enabled in the hw
>   state but doesn't have fb/crtc set in the plane_state force-disable it.
Can we disable those planes without penalty? Some of them call watermark update, this is a bug but still..

> We already do something similar with the vga plane, which we don't
> represent at all in kms.
>
> Then none of that initial modeset stuff would ever leak into an atomic
> modeset since it would be all contained in sanitize_crtc.
Ok.

~Maarten

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