Re: Revert "video: fbdev: mxsfb: Remove driver"

[Marek Vasut]

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) ?