linux-kernel - Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE

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Message-ID: <87mv7dfjjy.fsf@keithp.com>
Date:   Sat, 05 Aug 2017 23:42:57 -0400
From:   "Keith Packard" <keithp@...thp.com>
To:     Michel Dänzer <michel@...nzer.net>,
        Dave Airlie <airlied@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE ioctls [v2]

Michel Dänzer <michel@...nzer.net> writes:

> [...]
>
>> +#define DRM_CRTC_SEQUENCE_NEXT_ON_MISS		0x00000002	/* Use next sequence if we've missed */
>
> Do you have userspace making use of DRM_CRTC_SEQUENCE_NEXT_ON_MISS? If
> not, drop it.

I added this so that the new ioctl would be compatible with the old
ioctl; do you think that's unnecessary?
>
>> +#define DRM_CRTC_SEQUENCE_FIRST_PIXEL_OUT	0x00000004	/* Signal when first pixel is displayed */
>
> I thought there was consensus that this flag is pointless.

I just wrote a note to Daniel about this; I think it is useful in that
applications could specify that they actually want the event delivered
at first pixel out in accordance with the Vulkan spec, even if we can't
do that (yet). I definitely agree that requiring the bit be set is
ridiculous and should be removed.

Two choices

 1) Remove the code which checks whether the flag is set.
    Make Vulkan set the flag signaling what it wants.
    Plan on doing the actual driver work if we find that it's necessary.

 2) Remove the flag entirely.

Any preference?

-- 
-keith

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