linux-kernel - Re: [PATCH v3 3/3] drm/tiny: ili9486: remove conflicting framebuffers

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Message-ID: <9ec0204d-ca4c-afd9-33d6-1ebaaaf6b144@baylibre.com>
Date:   Tue, 6 Dec 2022 14:00:51 +0100
From:   Carlo Caione <ccaione@...libre.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>, neil.armstrong@...aro.org,
        Daniel Vetter <daniel@...ll.ch>,
        Jerome Brunet <jbrunet@...libre.com>,
        David Airlie <airlied@...il.com>,
        Kamlesh Gurudasani <kamlesh.gurudasani@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Kevin Hilman <khilman@...libre.com>
Cc:     linux-amlogic@...ts.infradead.org, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/3] drm/tiny: ili9486: remove conflicting framebuffers

On 06/12/2022 10:52, Thomas Zimmermann wrote:

>> Conflicting framebuffer on the SPI display ? How is that possible ?
> 
> Calling drm_aperture_remove_framebuffers() is only required if the 
> graphics card may have been pre-initialized by the system, such as a 
> VGA-compatible card on a PC.
> 
> Could the SPI display have been initialized by the firmware? If not, the 
> call should be left out.

What's happening on this board is that the builtin simpledrm driver is 
creating fb0 backed by the framebuffer prepared by u-boot / grub, and 
this the framebuffer being used by fbcon at early boot.

When the ILI9486 DRM driver is probed later during boot a second 
framebuffer is created (fb1) and when fb0 is destroyed, fbcon still 
remains attached to a non-existent framebuffer, so the user is left in 
the dark.

What this patch is doing is that when the ILI driver is probed, fb0 is 
destroyed and a new DRM-backed fb0 is created by the ILI DRM driver that 
can be used by fbcon, so the user can correctly see the console on the 
SPI display.

Cheers,

-- 
Carlo Caione