On 2021-08-12 9:49 p.m., Mark Yacoub wrote: > From: Mark Yacoub <markyacoub@xxxxxxxxxx> > > [Why] > Userspace should get back a copy of drm_wait_vblank that's been modified > even when drm_wait_vblank_ioctl returns a failure. > > Rationale: > drm_wait_vblank_ioctl modifies the request and expects the user to read > it back. When the type is RELATIVE, it modifies it to ABSOLUTE and updates > the sequence to become current_vblank_count + sequence (which was > RELATIVE), but now it became ABSOLUTE. > drmWaitVBlank (in libdrm) expects this to be the case as it modifies > the request to be Absolute so it expects the sequence to would have been > updated. > > The change is in compat_drm_wait_vblank, which is called by > drm_compat_ioctl. This change of copying the data back regardless of the > return number makes it en par with drm_ioctl, which always copies the > data before returning. > > [How] > Return from the function after everything has been copied to user. > > Fixes: IGT:kms_flip::modeset-vs-vblank-race-interruptible > Tested on ChromeOS Trogdor(msm) > > Signed-off-by: Mark Yacoub <markyacoub@xxxxxxxxxxxx> > Change-Id: I98da279a5f1329c66a9d1e06b88d40b247b51313 With the Gerrit Change-Id removed, Reviewed-by: Michel Dänzer <mdaenzer@xxxxxxxxxx> -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and X developer
