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Message-ID: <9ec0204d-ca4c-afd9-33d6-1ebaaaf6b144@baylibre.com>
Date:   Tue, 6 Dec 2022 14:00:51 +0100
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Subject: Re: [PATCH v3 3/3] drm/tiny: ili9486: remove conflicting framebuffers
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To:     Thomas Zimmermann <tzimmermann@suse.de>, neil.armstrong@linaro.org,
        Daniel Vetter <daniel@ffwll.ch>,
        Jerome Brunet <jbrunet@baylibre.com>,
        David Airlie <airlied@gmail.com>,
        Kamlesh Gurudasani <kamlesh.gurudasani@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
        Kevin Hilman <khilman@baylibre.com>
Cc:     linux-amlogic@lists.infradead.org, dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20221116-s905x_spi_ili9486-v3-0-59c6b58cbfe3@baylibre.com>
 <20221116-s905x_spi_ili9486-v3-3-59c6b58cbfe3@baylibre.com>
 <14e5c4e4-30dd-8efd-81e4-d680664ab04a@linaro.org>
 <c460bbda-6e9d-24e8-eb73-2e7207958deb@suse.de>
From:   Carlo Caione <ccaione@baylibre.com>
In-Reply-To: <c460bbda-6e9d-24e8-eb73-2e7207958deb@suse.de>
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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