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

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Date:   Wed, 17 Oct 2018 09:43:15 -0300
From:   Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
To:     Gustavo Padovan <gustavo@...ovan.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH v2] drm/drm_vblank: Change EINVAL by the correct errno

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?

Another question, do I need to send a V3 with intel-gfx-ci?
 
> 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.

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