Quoting Rodrigo Siqueira (2018-10-08 15:52:20) > For historical reason, the function drm_wait_vblank_ioctl always return > -EINVAL if something gets wrong. This scenario limits the flexibility > for the userspace make detailed verification of the problem and take > some action. In particular, the validation of “if (!dev->irq_enabled)” > in the drm_wait_vblank_ioctl is responsible for checking if the driver > support vblank or not. If the driver does not support VBlank, the > function drm_wait_vblank_ioctl returns EINVAL which does not represent > the real issue; this patch changes this behavior by return ENOTTY > (Inappropriate ioctl for device). Additionally, some operations are > unsupported by this function, and returns EINVAL; this patch changes the > return value to EOPNOTSUPP (Operation not supported). Lastly, the > function drm_wait_vblank_ioctl is invoked by libdrm, which is used by > many compositors; because of this, it is important to check if this > change breaks any compositor. In this sense, the following projects were > examined: > > * Drm-hwcomposer > * Kwin > * Sway > * Wlroots > * Wayland-core > * Weston > * Xorg (67 different drivers) > > For each repository the verification happened in three steps: > > * Update the main branch > * Look for any occurrence "drmWaitVBlank" with the command: > git grep -n "drmWaitVBlank" > * Look in the git history of the project with the command: > git log -SdrmWaitVBlank > > Finally, none of the above projects validate the use of EINVAL which > make safe, at least for these projects, to change the return values. > > Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx> > --- > drivers/gpu/drm/drm_vblank.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c > index 98e091175921..88ec6fb49afb 100644 > --- a/drivers/gpu/drm/drm_vblank.c > +++ b/drivers/gpu/drm/drm_vblank.c > @@ -1533,10 +1533,10 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data, > unsigned int flags, pipe, high_pipe; > > if (!dev->irq_enabled) > - return -EINVAL; > + return -ENOTTY; Arguable. > > if (vblwait->request.type & _DRM_VBLANK_SIGNAL) > - return -EINVAL; User error -> einval. > + return -EOPNOTSUPP; > > if (vblwait->request.type & > ~(_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK | > @@ -1545,7 +1545,7 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data, > vblwait->request.type, > (_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK | > _DRM_VBLANK_HIGH_CRTC_MASK)); > - return -EINVAL; > + return -EOPNOTSUPP; User error -> einval. -Chris
