linux-kernel - Re: [PATCH v3 2/2] drm/fb-helper: implement ioctl FBIO

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Date:   Wed, 22 Feb 2017 16:05:31 +0900
From:   Michel Dänzer <michel@...nzer.net>
To:     Stefan Lengfeld <contact@...fanchrist.eu>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH v3 2/2] drm/fb-helper: implement ioctl FBIO_WAITFORVSYNC

On 21/02/17 07:00 PM, Stefan Lengfeld wrote:
> 
> 2/ Wait for a single vsync event on all active crtcs as Ville Syrjälä 
>    described here [2] in the optimal implementation.

FWIW, this seems like a bad idea, since with multiple active CRTCs it
would make it essentially random at which intervals the ioctl returns,
and which CRTCs are in vertical blank when it does. So it would be
useless for both timing and tearing prevention purposes, i.e. more or
less completely useless.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer