linux-kernel - [BUG] SPI broken for SPI based panel drivers

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Date:   Mon, 30 Nov 2020 20:03:23 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: [BUG] SPI broken for SPI based panel drivers

Hi,
starting from v5.10-rc5 the SPI based panel of the GTA04 device is broken. It uses
compatible = "spi-gpio"; [1] i.e. gpio descriptors very indirectly.

Bisect shows that it is commit

766c6b63aa04 ("spi: fix client driver breakages when using GPIO descriptors")

The commit description tells about a problematic pattern and indeed the driver is
using it - like ca. 15 other spi based panel drivers in drivers/gpu/drm/panel/

I understood that it wants to fix the spi system to handle that correctly again.
But reverting your patch brings back the display. So it appears as if it does not
fix a breakage, rather breaks a previously working setup.

What should we do?

BR and thanks,
Nikolaus

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap3-gta04.dtsi?h=v5.10-rc6#n107