linux-kernel - Re: [PATCH] drm/fb-helper: Blacklist writeback when adding connectors to fbdev

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Date:   Wed, 21 Nov 2018 10:40:17 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Sean Paul <sean@...rly.run>
Subject: Re: [PATCH] drm/fb-helper: Blacklist writeback when adding
 connectors to fbdev

On Mon, Nov 19, 2018 at 10:28:35AM +0100, Maxime Ripard wrote:
> On Thu, Nov 15, 2018 at 05:32:48PM +0100, Paul Kocialkowski wrote:
> > Writeback connectors do not produce any on-screen output and require
> > special care for use. Such connectors are hidden from enumeration in
> > DRM resources by default, but they are still picked-up by fbdev.
> > This makes rather little sense since fbdev is not really adapted for
> > dealing with writeback.
> > 
> > Moreover, this is also a source of issues when userspace disables the
> > CRTC (and associated plane) without detaching the CRTC from the
> > connector (which is hidden by default). In this case, the connector is
> > still using the CRTC, leading to am "enabled/connectors mismatch" and
> > eventually the failure of the associated atomic commit. This situation
> > happens with VC4 testing under IGT GPU Tools.
> > 
> > Filter out writeback connectors in the fbdev helper to solve this.
> > 
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> 
> Reviewed-by: Maxime Ripard <maxime.ripard@...tlin.com>
> Tested-by: Maxime Ripard <maxime.ripard@...tlin.com>

Applied with a cc: stable to drm-misc-fixes. Btw, 2 r-b from committers,
someone should have pushed this I think :-)

Thanks for patch&review.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch