Hi Am 20.04.21 um 10:46 schrieb Daniel Vetter:
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@xxxxxxx> 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?
Offb doesn't seem to be tied to the simple-framebuffer support. So adding a new driver or extending the simple-framebuffer code would be required. Not a big deal, though. Patch 3 of this patchset adds the ability to create generic drivers within DRM.
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.
I think we can just use a shadow palette in the drm driver: If the drm framebuffer is in C8, use the userspace's palette. If the drm framebuffer is in XRGB, use a palette that represents RGB332. The driver would do on-the-fly conversion; just like cirrus does.
Best regards Thomas
-Daniel
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer
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