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SubjectRe: [PATCH] drm: mxsfb: check framebuffer pitch
On Mon, Sep 07, 2020 at 07:17:12PM +0300, Laurent Pinchart wrote:
> Hi Stefan,
>
> Thank you for the patch.
>
> On Mon, Sep 07, 2020 at 06:03:43PM +0200, Stefan Agner wrote:
> > The lcdif IP does not support a framebuffer pitch (stride) other than
> > the CRTC width. Check for equality and reject the state otherwise.
> >
> > This prevents a distorted picture when using 640x800 and running the
> > Mesa graphics stack. Mesa tires to use a cache aligned stride, which
>
> s/tires/tries/
>
> > leads at that particular resolution to width != stride. Currently
> > Mesa has no fallback behavior, but rejecting this configuration allows
> > userspace to handle the issue correctly.
>
> I'm increasingly impressed by how featureful this IP core is :-)
>
> > Signed-off-by: Stefan Agner <stefan@agner.ch>
> > ---
> > drivers/gpu/drm/mxsfb/mxsfb_kms.c | 22 ++++++++++++++++++----
> > 1 file changed, 18 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > index b721b8b262ce..79aa14027f91 100644
> > --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > @@ -403,14 +403,28 @@ static int mxsfb_plane_atomic_check(struct drm_plane *plane,
> > {
> > struct mxsfb_drm_private *mxsfb = to_mxsfb_drm_private(plane->dev);
> > struct drm_crtc_state *crtc_state;
> > + unsigned int pitch;
> > + int ret;
> >
> > crtc_state = drm_atomic_get_new_crtc_state(plane_state->state,
> > &mxsfb->crtc);
> >
> > - return drm_atomic_helper_check_plane_state(plane_state, crtc_state,
> > - DRM_PLANE_HELPER_NO_SCALING,
> > - DRM_PLANE_HELPER_NO_SCALING,
> > - false, true);
> > + ret = drm_atomic_helper_check_plane_state(plane_state, crtc_state,
> > + DRM_PLANE_HELPER_NO_SCALING,
> > + DRM_PLANE_HELPER_NO_SCALING,
> > + false, true);
> > + if (ret || !plane_state->visible)
>
> Would it be more explict to check for !plane_state->fb ? Otherwise I'll
> have to verify that !fb always implies !visible :-)
>
> > + return ret;
> > +
> > + pitch = crtc_state->mode.hdisplay *
> > + plane_state->fb->format->cpp[0];
>
> This holds on a single line.
>
> > + if (plane_state->fb->pitches[0] != pitch) {
> > + dev_err(plane->dev->dev,
> > + "Invalid pitch: fb and crtc widths must be the same");
>
> I'd turn this into a dev_dbg(), printing error messages to the kernel
> log in response to user-triggered conditions is a bit too verbose and
> could flood the log.
>
> Wouldn't it be best to catch this issue when creating the framebuffer ?

Yeah this should be verified at addfb time. We try to validate as early as
possible.
-Daniel

>
> > + return -EINVAL;
> > + }
> > +
> > + return 0;
> > }
> >
> > static void mxsfb_plane_primary_atomic_update(struct drm_plane *plane,
>
> --
> Regards,
>
> Laurent Pinchart

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

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