On Tue, Sep 4, 2018 at 11:02 AM, Michel Dänzer michel@daenzer.net wrote:
On 2018-09-04 3:05 p.m., Ilia Mirkin wrote:
On Tue, Sep 4, 2018 at 4:00 AM, Michel Dänzer michel@daenzer.net wrote:
On 2018-09-03 7:07 p.m., Ilia Mirkin wrote:
On Mon, Sep 3, 2018 at 12:45 PM, Daniel Vetter daniel@ffwll.ch 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@redhat.com
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. :)
Right, but ADDFB doesn't know or care about DRM_FORMAT_*. That's what I'm saying -- keep ADDFB working, and fix up the DRM_FORMAT_* underneath it both in the conversion and in the driver. Gerd's patch allows us to do this incrementally, eventually truing up the DRM_FORMAT_* in the driver, enabling ADDFB2 to work as expected.
-ilia