linux-kernel - Re: Revert "video: fbdev: mxsfb: Remove driver"

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Date:   Sun, 15 Aug 2021 14:31:37 +0200
From:   Marek Vasut <marex@...x.de>
To:     Alistair Francis <alistair23@...il.com>,
        Fabio Estevam <festevam@...il.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>, b.zolnierkie@...sung.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alistair Francis <alistair@...stair23.me>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: Revert "video: fbdev: mxsfb: Remove driver"

On 8/15/21 2:16 PM, Alistair Francis wrote:
> Hello,
> 
> Commit f225f1393f034 "video: fbdev: mxsfb: Remove driver" removed the
> mxsfb fbdev driver.
> 
> I am now working on getting mainline Linux running on the reMarkable 2
> eInk reader [1]. Unfortunately the rM2 doesn't use the standard EPD
> controller on the i.MX SoC, but instead uses the LCD controller.
> 
> eInk panels are complex to control and require writing temperature
> dependent waveforms. As these waveforms are proprietary [2] the rM
> team runs closed source software called SWTCON in userspace to control
> the panel [3].
> 
> This closed source software expects the fbdev mxsfb driver and it
> doesn't work with the DRM mxsfb driver (at least not that I can get it
> to).
> 
> The NXP fork of Linux also re-adds the fbdev driver [4], so they also
> see some uses for it.
> 
> I was wondering if the community would be open to re-adding the fbdev
> mxsfb driver to mainline? It could be re-added with a different
> dt-binding so that it is not used by default and only enabled for
> boards when required (like for the rM2).
> 
> 1: https://remarkable.com/store/remarkable-2
> 2: https://goodereader.com/blog/e-paper/e-ink-waveforms-are-a-closely-guarded-secret
> 3: https://remarkablewiki.com/tech/rm2_framebuffer
> 4: https://source.codeaurora.org/external/imx/linux-imx/log/drivers/video/fbdev/mxsfb.c?h=lf-5.10.35-2.0.0

+CC Sam.

What sort of special thing does your proprietary userspace do that 
cannot be added to the DRM driver or the fbdev emulation (if needed) ?