Hi Gerd, On Thu, Nov 24, 2022 at 8:29 AM Gerd Hoffmann <kraxel@xxxxxxxxxx> wrote: > > > > +#ifdef __BIG_ENDIAN > > > > > > Why do we need the #ifdef here? Iirc some hw has big endian flags in the > > > scanout registers, so could supprt this unconditionally if there's no > > > #ifdef around the format defines. Some drivers might then also want a > > > DRM_FORMAT_FOO_BE define to simplify tables and stuff, but that's more a > > > bikeshed. > > > > "Limit this to big-endian platforms, as there is currently no need > > to support these formats on little-endian platforms." > > > > Will anyone make use of this? In theory, all of the 16-bpp formats > > can have a big-endian counterpart. > > Highly unlikely. Dealing with 16-bpp formats in non-native byte order > is a PITA because it isn't enough to simply adjust the masks and shifts > to pick the correct bits and be done with it. > > The qemu stdvga happens to have a register to switch framebuffer > byteorder (so both x64 and ppc are happy), and the bochs drm driver > actually supports that no matter what the cpu byte order is, but it > supports only DRM_FORMAT_XRGB8888 + DRM_FORMAT_BGRX8888. > > Supporting 16 bpp in the driver wouldn't be that much of a problem, but > processing the framebuffer on the host side when emulating a big endian > guest on a little endian host is painful. I think I can't ask pixman to > do a conversation from DRM_FORMAT_RGB565 | DRM_FORMAT_BIG_ENDIAN to > DRM_FORMAT_XRGB8888 on a little endian machine. Indeed. But you can do a quick 16-bit byteswap, and convert from DRM_FORMAT_RGB565 to DRM_FORMAT_XRGB8888? There's a similar issue with Cairo, cfr. '[PATCH libdrm v2 08/10] util: Fix pwetty on big-endian"[1]. BTW, does pixman support converting DRM_FORMAT_RGB565 to DRM_FORMAT_XRGB8888 on a big-endian machine? [1] https://lore.kernel.org/all/e8597038478f12e9eda5e86b309b52988f69f2eb.1657302103.git.geert@xxxxxxxxxxxxxx Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
