[PATCH v2] Partially revert "video: fbdev: amba-clcd: Retire elder CLCD driver"

[Linus Walleij]

On Tue, Sep 29, 2020 at 9:53 PM Peter Collingbourne <pcc at google.com> wrote:

> The fbdev driver is used by Android's FVP configuration. Using the
> DRM driver together with DRM's fbdev emulation results in a failure
> to boot Android. The root cause is that Android's generic fbdev
> userspace driver relies on the ability to set the pixel format via
> FBIOPUT_VSCREENINFO, which is not supported by fbdev emulation.
>
> There have been other less critical behavioral differences identified
> between the fbdev driver and the DRM driver with fbdev emulation. The
> DRM driver exposes different values for the panel's width, height and
> refresh rate, and the DRM driver fails a FBIOPUT_VSCREENINFO syscall
> with yres_virtual greater than the maximum supported value instead
> of letting the syscall succeed and setting yres_virtual based on yres.

Is there a way to reproduce this? A simple binary image where
we can start Android on FVP and just replace the kernel image
would be great. That way we can look at the incompatibilities
in the FBDEV emulation and try to fix them.

Is it working with a stock kernel or do you need any out-of-tree
Android patches to run this?

Can you also share the kernel config used for this build so it is
easy to rebuild a similar kernel?

Yours,
Linus Walleij