Re: [PATCH v4 0/9] drm: Support simple-framebuffer devices and firmware fbs

Daniel Vetter
2021-04-20T08:46:55Z

On Mon, Apr 19, 2021 at 10:00:56AM +0200, Geert Uytterhoeven wrote:
> Hi Thomas,
>
> On Fri, Apr 16, 2021 at 11:00 AM Thomas Zimmermann <tzimmermann@suse.de> wrote:
> > This patchset adds support for simple-framebuffer platform devices and
> > a handover mechanism for native drivers to take-over control of the
> > hardware.
> >
> > The new driver, called simpledrm, binds to a simple-frambuffer platform
> > device. The kernel's boot code creates such devices for firmware-provided
> > framebuffers, such as EFI-GOP or VESA. Typically the BIOS, UEFI or boot
> > loader sets up the framebuffers. Description via device tree is also an
> > option.
>
> I guess this can be used as a replacement for offb, too...
>
> > Patches 4 to 8 add the simpledrm driver. It's build on simple DRM helpers
> > and SHMEM. It supports 16-bit, 24-bit and 32-bit RGB framebuffers. During
>
> .... if support for 8-bit frame buffers would be added?

Is that 8-bit greyscale or 8-bit indexed with 256 entry palette? Former
shouldn't be a big thing, but the latter is only really supported by the
overall drm ecosystem in theory. Most userspace assumes that xrgb8888
works, and we keep that illusion up by emulating it in kernel for hw which
just doesn't support it. But reformatting xrgb8888 to c8 is tricky at
best. The uapis are all there for setting the palette, and C8 is a defined
format even with atomic kms interface, but really there's not much
userspace for it. In other words, it would work as well as current offb
would, but that's at least that.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation