linux-kernel - Re: [PATCH v2] drm/drm_vblank: Change EINVAL by the correct errno

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Message-ID: <20190113202323.co7upmn5fg32b7gn@smtp.gmail.com>
Date:   Sun, 13 Jan 2019 18:23:23 -0200
From:   Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     Gustavo Padovan <gustavo@...ovan.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <sean@...rly.run>, Dave Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH v2] drm/drm_vblank: Change EINVAL by the correct errno

Hi,

I resend this patch for CI via “intel-gfx@...ts.freedesktop.org” as
Daniel suggested, and I got a feedback that reported an issue as can be
seen here:

   https://patchwork.freedesktop.org/series/51147/

After a careful analysis of what happened, I concluded that the problem
is related to the function “igt_wait_for_vblank_count()” in “igt_kms.c”.
This function has the following assert:

   igt_assert(drmWaitVBlank(drm_fd, &wait_vbl) == 0)

This function only checks if everything went well with the
drmWaitVBlank() operation and does not make any other validation. IMHO
the patch is correct, and the problem pointed out by CI is not related
to this change.

Make sense?

Best Regards

On 10/17, Daniel Vetter wrote:
> On Wed, Oct 17, 2018 at 2:43 PM Rodrigo Siqueira
> <rodrigosiqueiramelo@...il.com> wrote:
> >
> > Hi,
> >
> > First of all, thanks to all for the reviewers and feedbacks.
> >
> > On 10/16, Daniel Vetter wrote:
> > > 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@...il.com>
> > >
> > > Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
> > >
> > > Can you pls also let intel-gfx-ci test this patch? You just need to
> > > include intel-gfx@...ts.freedesktop.org in your recipient list.
> >
> > I did know about intel-gfx-ci, really nice:)
> >
> > Should I CC this mailing list if I send patches to the DRM core, amdgpu,
> > i915, vc4, vgem, and virtio-gpu? I suppose that IGT is running on the
> > CI, right?
> 
> It's only intel gpus (well and one special amd one) running igt on a
> _lot_ of different machines.
> 
> > Another question, do I need to send a V3 with intel-gfx-ci?
> 
> If the patch-set is unchanged people use the "FOR CI" subject prefix
> when resending, instead of incrementing the version number.
> 
> > > 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
> >
> > Yes, I want :)
> > I will need some guidance, in the beginning, to get confident about the
> > processes. If you can help me with this, I will be glad to play around
> > with 'dim' and the merging tasks.
> 
> Sure, just ping me on irc. First you need a freedesktop.org ssh account:
> 
> https://www.freedesktop.org/wiki/AccountRequests/
> 
> You need to request access to the drm-misc group. Once you have the
> bugzilla, pls ping me so I can ack it.
> 
> Thanks, Daniel
> 
> >
> > Best Regards
> >
> > > 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
> >
> > --
> > Rodrigo Siqueira
> > https://siqueira.tech
> > https://twitter.com/siqueirajordao
> > Graduate Student
> > Department of Computer Science
> > University of São Paulo
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@...ts.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch

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