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    SubjectRe: [PATCH v2] drm/drm_vblank: Change EINVAL by the correct errno
    On Mon, Oct 15, 2018 at 02:05:29PM -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 V1:
    > Daniel Vetter and Chris Wilson
    > - Replace ENOTTY by EOPNOTSUPP
    > - Return EINVAL if the parameters are wrong
    >
    > Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>

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

    Can you pls also let intel-gfx-ci test this patch? You just need to
    include intel-gfx@lists.freedesktop.org in your recipient list.

    For merging, since you plan to stick around doing kms stuff a bit: Want
    commit rights for drm-misc?

    https://drm.pages.freedesktop.org/maintainer-tools/getting-started.html

    Cheers, Daniel

    > ---
    > 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 98e091175921..80f5a3bb427e 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 -EOPNOTSUPP;
    >
    > if (vblwait->request.type & _DRM_VBLANK_SIGNAL)
    > - return -EINVAL;
    > + return -EOPNOTSUPP;
    >
    > if (vblwait->request.type &
    > ~(_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK |
    > --
    > 2.19.1

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

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