Re: [PATCH v2] drm/atomic: Fix bookkeeping with TEST_ONLY, v2.

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

Op 27-08-15 om 15:50 schreef Ville Syrjälä:
> On Thu, Aug 27, 2015 at 03:05:38PM +0200, Maarten Lankhorst wrote:
>> Op 27-08-15 om 14:52 schreef Ville Syrjälä:
>>> On Thu, Aug 27, 2015 at 02:50:34PM +0200, Maarten Lankhorst wrote:
>>>> Op 27-08-15 om 14:48 schreef Ville Syrjälä:
>>>>> On Thu, Aug 27, 2015 at 02:43:35PM +0200, Maarten Lankhorst wrote:
>>>>>> Op 27-08-15 om 14:19 schreef Daniel Stone:
>>>>>>> Hi,
>>>>>>>
>>>>>>> On 4 August 2015 at 12:34, Maarten Lankhorst
>>>>>>> <maarten.lankhorst@linux.intel.com> wrote:
>>>>>>>> Commit ec9f932ed41622d120de52a5b525e4d77b9ef17e
>>>>>>>> "drm/atomic: Cleanup on error properly in the atomic ioctl."
>>>>>>>> cleaned up some error paths, but didn't fix the TEST_ONLY path.
>>>>>>>> In the check only case plane->fb shouldn't be updated, and
>>>>>>>> the vblank events should be cleared as on failure.
>>>>>>> Bikeshedding a bit ...
>>>>>>>
>>>>>>> An early test precludes TEST_ONLY | PAGE_FLIP_EVENT, so you don't need
>>>>>>> to mention this in the commit message; in this case, the main change
>>>>>>> is about plane->{,old_}fb.
>>>>>> Even testing with PAGE_FLIP_EVENT would be useful because
>>>>>> event && !crtc_state->active should not be allowed. In that case test
>>>>>> could succeed but commit could fail.
>>>>> Why would commit fail when the we're in DPMS off? I would suggest it
>>>>> should be allowed. The operation would just a be a nop from a HW point
>>>>> of view, all the calculation/checks would still be performed.
>>>>>
>>>> You can commit, just not with PAGE_FLIP_EVENT set when crtc is inactive.
>>> What's so special about the event here? Just send it out as soon as the
>>> state has been swapped.
>> Previously this has been disallowed for legacy page flips.
> I don't think so. Speaking for i915, I think we've just rejected legacy page
> flips entirely with the pipe is off on account of drm_vblank_get() failing.
No atomic driver handles this case correctly. You can't get vblank events with the crtc off.
>> I don't see why this should be relaxed. It just complicates things and you have nothing to stick in for the vblank counter.
> We could stick the last vbl count/timestamp in there.
>
> Not allowing means userspace is forced to consider the dpms state
> whenever it wants to call the atomic ioctl.
Userspace was the one turning off the crtc in the first place; it shouldn't continue flipping but preserve power. :-)

~Maarten
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