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

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Message-ID: <20181119092835.3y2xqfclwlmk4cww@flea>
Date:   Mon, 19 Nov 2018 10:28:35 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Eric Anholt <eric@...olt.net>,
        Boris Brezillon <boris.brezillon@...tlin.com>
Subject: Re: [PATCH] drm/fb-helper: Blacklist writeback when adding
 connectors to fbdev

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>

Thanks!
Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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