On 2018-09-04 3:05 p.m., Ilia Mirkin wrote: > On Tue, Sep 4, 2018 at 4:00 AM, Michel Dänzer <michel@xxxxxxxxxxx> wrote: >> On 2018-09-03 7:07 p.m., Ilia Mirkin wrote: >>> On Mon, Sep 3, 2018 at 12:45 PM, Daniel Vetter <daniel@xxxxxxxx> wrote: >>>> On Mon, Sep 03, 2018 at 12:57:54PM +0200, Gerd Hoffmann wrote: >>>>> Userspace on big endian machhines typically expects the ADDFB ioctl >>>>> returns a big endian framebuffer. drm_mode_addfb() will call >>>>> drm_mode_addfb2() unconditionally with little endian DRM_FORMAT_* >>>>> values though, which is wrong. This patch fixes that. >>>>> >>>>> Drivers (both kernel and xorg) have quirks in place to deal with the >>>>> broken drm_mode_addfb() behavior. Because of this we can't just change >>>>> drm_mode_addfb() behavior for everybody without breaking things. So add >>>>> a new driver feature flag DRIVER_PREFER_HOST_BYTE_ORDER, so drivers can >>>>> opt-in. >>>>> >>>>> Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx> >>>>> --- >>>>> include/drm/drm_drv.h | 1 + >>>>> drivers/gpu/drm/drm_framebuffer.c | 11 +++++++++++ >>>>> 2 files changed, 12 insertions(+) >>>>> >>>>> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h >>>>> index 46a8009784..9cf12596cd 100644 >>>>> --- a/include/drm/drm_drv.h >>>>> +++ b/include/drm/drm_drv.h >>>>> @@ -57,6 +57,7 @@ struct drm_printer; >>>>> #define DRIVER_KMS_LEGACY_CONTEXT 0x20000 >>>>> #define DRIVER_SYNCOBJ 0x40000 >>>>> #define DRIVER_PREFER_XBGR_30BPP 0x80000 >>>>> +#define DRIVER_PREFER_HOST_BYTE_ORDER 0x100000 >>>> >>>> Hm, not a huge fan of using driver_flags for random little quirks. I think >>>> a boolean in sturct drm_mode_config would be much better. Bonus if you >>>> also move the 30bpp hack over to that. Something like >>>> mode_config.quirk_addfb_host_byte_order and >>>> mode_config.quirk_addfb_prefer_xbgr_30bpp or whatever. That has the upside >>>> of giving us a really nice place to put a huge comment about what this is >>>> supposed to do. >>>> >>>> I think otherwise this looks overall rather reasonable. I think the only >>>> other driver that ever cared about big endian was radeon/amdgpu. Would be >>>> good to get at least an ack from amd folks, or a "meh, stopped caring". >>> >>> and nouveau. >>> >>> I do believe that ADDFB should be made to always prefer host byte >>> order -- this is how all of the existing implementations work in >>> practice. However e.g. nouveau wants DRM_FORMAT_XRGB8888. But it still >>> treats it as host byte order. This will become more important in a >>> world where ADDFB2 is more common. >>> >>> So, I think that this change should be applied, drivers (I suspect >>> just nouveau and radeon) fixed up to consume the "new" formats, [...] >> >> As explained before, that would break radeon userspace on big endian hosts. > > We last discussed this about a year ago, so I hope you'll forgive my > lapse in memory... > > There's userspace that uses ADDFB2 with DRM_FORMAT_XRGB8888 but > expects it to be host-endian? ADDFB, not ADDFB2. The latter probably didn't even exist yet when this was made to work. :) -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
