Re: [RESEND PATCH V3] drm/drm_vblank: Change EINVAL by the correct errno

Daniel Vetter
2019-06-13T08:21:47Z

On Wed, Jun 12, 2019 at 11:10:54PM -0300, Rodrigo Siqueira wrote:
> 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 EOPNOTSUPP.
> Additionally, some operations are unsupported by this function, and
> returns EINVAL; this patch also changes the return value to EOPNOTSUPP
> in this case. 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.
>
> Change since V2:
> Daniel Vetter and Chris Wilson
> - Replace ENOTTY by EOPNOTSUPP
> - Return EINVAL if the parameters are wrong
>
> Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
> ---
> Update:
> Now IGT has a way to validate if a driver has vblank support or not.
> See: https://gitlab.freedesktop.org/drm/igt-gpu-tools/commit/2d244aed69165753f3adbbd6468db073dc1acf9A
>
> drivers/gpu/drm/drm_vblank.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 0d704bddb1a6..d76a783a7d4b 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -1578,10 +1578,10 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
> unsigned int flags, pipe, high_pipe;
>
> if (!dev->irq_enabled)
> - return -EINVAL;
> + return -EOPNOTSUPP;
>
> if (vblwait->request.type & _DRM_VBLANK_SIGNAL)
> - return -EINVAL;
> + return -EOPNOTSUPP;

Not sure we want EINVAL here, that's kinda a "parameters are wrong"
version too. With that changed:

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

>
> if (vblwait->request.type &
> ~(_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK |
> --
> 2.21.0

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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