linux-kernel - Re: [PATCH v3 7/7] [wip] virtio-gpu: add page flip support

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Date:	Tue, 31 May 2016 09:39:04 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Gerd Hoffmann <kraxel@...hat.com>
Cc:	dri-devel <dri-devel@...ts.freedesktop.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:VIRTIO GPU DRIVER" 
	<virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH v3 7/7] [wip] virtio-gpu: add page flip support

On Tue, May 31, 2016 at 9:34 AM, Gerd Hoffmann <kraxel@...hat.com> wrote:
>   Hi,
>
>> > Right now the virtual outputs are linked to drm_crtc.  To apply any
>> > changes I need to lookup the crtc to figure which virtual output should
>> > be updated.
>
>> > So, setting active_only should make sure I have a valid crtc pointer on
>> > plane updates, right?  It probably also skips the disable + enable crtc
>> > steps on commit?  What happens when outputs are disabled?
>
>> Nah, I just misunderstood your patch. If it's all about finding the
>> corresponding crtc, then you're all good.
>
> Yes, it's all about finding the crtc.
>
>> I thought there was some
>> other reason (like the virtual hw getting upset about certain things).
>
> virtio wouldn't be upset.
>
> It's a pointless exercise though to first disable the output, just to
> re-enable it the next moment with the new page-flipped framebuffer.  So
> I guess I should look at the active_only thing nevertheless.

It's still possible that the plane can get disabled without it getting
enabled. Userspace is allowed to do this. But since this suprises a
lot of driver writers there's a special atomic_plane_disable hook you
can use for the disable path. Instead of hand-rolling that check in
your own code.

>> btw can you pls drop an ack or r-b
>> onto my virtio conversion? I already added your tested-by.
>
> Grr, mail is not in my dri-devel folder.  Guess that is the <censored>
> "avoid-duplicates" mailman option at work.
>
> Feel free to just add the r-b too.  Or I'll send it for the next version
> of the series.

Added your r-b locally so it won't get lost on the next round.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch