Re: [PATCH] drm: mxsfb: check framebuffer pitch

[Daniel Vetter]

On Tue, Sep 8, 2020 at 2:07 PM Stefan Agner <stefan@xxxxxxxx> wrote:
>
> On 2020-09-08 10:48, Daniel Vetter wrote:
> > On Tue, Sep 08, 2020 at 11:18:25AM +0300, Tomi Valkeinen wrote:
> >> Hi,
> >>
> >> On 08/09/2020 10:55, Stefan Agner wrote:
> >> > On 2020-09-07 20:18, Daniel Vetter wrote:
> >> >> 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@xxxxxxxx>
> >> >>>> ---
> >> >>>>  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
> >> >>
> >> >
> >> > Sounds sensible. From what I can tell fb_create is the proper callback
> >> > to implement this at addfb time. Will give this a try.
> >> >
> >> > FWIW, I got the idea from drivers/gpu/drm/tilcdc/tilcdc_plane.c. Maybe
> >> > should be moved to addfb there too?
> >>
> >> But you don't know the crtc width when creating the framebuffer.
> >
> > Hm right this is a different check. What we could check in fb_create for
> > both is that the logical fb size matches exactly the pitch. That's not
> > sufficient criteria, but it will at least catch some of them already.
> >
> > But yeah we'd need both here.
>
> After validating width of framebuffer against pitch, the only thing we
> need to check here is that the width matches. From what I can tell,
> least for mxsfb, this should be covered by
> drm_atomic_helper_check_plane_state's can_position parameter set to
> false.

This only checks against the src rectangle of the crtc state, there's
nothing forcing that the size of the fb matches the src rectangle
exactly. I guess we could maybe add that as another parameter for hw
like yours or tilcdc. Naming is a bit tricky, maybe
require_matching_fb or src_must_match_fb or something like that.

> So I think in my case I can get away by only checking the framebuffer.

You still need both I think.
-Daniel

>
> --
> Stefan
>
>
> > -Daniel
> >
> >>
> >>  Tomi
> >>
> >> --
> >> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
> >> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki



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