[PATCH V6] drm/drm_vblank: Change EINVAL by the correct errno

Rodrigo Siqueira rodrigosiqueiramelo at gmail.com
Wed Oct 2 14:05:16 UTC 2019

For historical reasons, the function drm_wait_vblank_ioctl always return
-EINVAL if something gets wrong. This scenario limits the flexibility
for the userspace to make detailed verification of any 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 EOPNOTSUPP.
Additionally, drm_crtc_get_sequence_ioctl and
drm_crtc_queue_sequence_ioctl, also returns EINVAL if vblank is not
supported; this patch also changes the return value to EOPNOTSUPP in
these functions. Lastly, these functions are 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
* Weston
* Mutter
* Xorg (67 different drivers)

For each repository the verification happened in three steps:

* Update the main branch
* Look for any occurrence of "drmCrtcQueueSequence",
  "drmCrtcGetSequence", and "drmWaitVBlank" with the command git grep -n
* Look in the git history of the project with the command
git log -S<STRING>

None of the above projects validate the use of EINVAL when using
drmWaitVBlank(), which make safe, at least for these projects, to change
the return values. On the other hand, mesa and xserver project uses
drmCrtcQueueSequence() and drmCrtcGetSequence(); this change is harmless
for both projects.

Change since V5 (Pekka Paalanen):
 - Check if the change also affects Mutter

Change since V4 (Daniel):
 - Also return EOPNOTSUPP in drm_crtc_[get|queue]_sequence_ioctl

Change since V3:
 - Return EINVAL for _DRM_VBLANK_SIGNAL (Daniel)

Change since V2:
 Daniel Vetter and Chris Wilson
 - Return EINVAL if the parameters are wrong

Cc: Keith Packard <keithp at keithp.com>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: Pekka Paalanen <pekka.paalanen at collabora.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo at gmail.com>
 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 9c6899758bc9..71cf2633ac58 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1610,7 +1610,7 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
 	unsigned int flags, pipe, high_pipe;
 	if (!dev->irq_enabled)
-		return -EINVAL;
+		return -EOPNOTSUPP;
 	if (vblwait->request.type & _DRM_VBLANK_SIGNAL)
 		return -EINVAL;
@@ -1876,7 +1876,7 @@ int drm_crtc_get_sequence_ioctl(struct drm_device *dev, void *data,
 		return -EOPNOTSUPP;
 	if (!dev->irq_enabled)
-		return -EINVAL;
+		return -EOPNOTSUPP;
 	crtc = drm_crtc_find(dev, file_priv, get_seq->crtc_id);
 	if (!crtc)
@@ -1934,7 +1934,7 @@ int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data,
 		return -EOPNOTSUPP;
 	if (!dev->irq_enabled)
-		return -EINVAL;
+		return -EOPNOTSUPP;
 	crtc = drm_crtc_find(dev, file_priv, queue_seq->crtc_id);
 	if (!crtc)
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