Re: [PATCH] drm/i915: Fix frontbuffer false positve.

Daniel Vetter
2015-02-24T22:07:46Z

On Tue, Feb 24, 2015 at 01:42:39PM -0800, Matt Roper wrote:
> On Tue, Feb 24, 2015 at 01:37:54PM -0800, Rodrigo Vivi wrote:
> > This return 0 without setting atomic bits on fb == crtc->cursor->fb
> > where causing frontbuffer false positives.
> >
> > According to Daniel:
> >
> > The original regression seems to have been introduced in the original
> > check/commit split:
> >
> > commit 757f9a3e5b8a812af0c213099a5b31cb423f4d3c
> > Author: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > Date: Wed Sep 24 14:20:24 2014 -0300
> >
> > drm/i915: move check of intel_crtc_cursor_set_obj() out
> >
> > Which already cause other trouble, resulting in the check getting moved in
> >
> > commit e391ea882b1a04fb3f559287ac694652a3cd9da9
> > Author: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > Date: Wed Sep 24 14:20:25 2014 -0300
> >
> > drm/i915: Fix not checking cursor and object sizes
> >
> > The frontbuffer tracking itself only was broken when we shifted it into
> > the check/commit logic with:
> >
> > commit 32b7eeec4d1e861230b09d437e95d76c86ff4a68
> > Author: Matt Roper <matthew.d.roper@intel.com>
> > Date: Wed Dec 24 07:59:06 2014 -0800
> >
> > drm/i915: Refactor work that can sleep out of commit (v7)
> >
> > v2: When putting more debug prints I notice the solution was simpler
> > than I thought. AMS design is solid, just this return was wrong.
> > Sorry for the noise.
> >
> > v3: Remove the entire chunck that would probably
> > be removed by gcc anyway. (by Daniel)
> >
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Cc: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > Cc: Matt Roper <matthew.d.roper@intel.com>
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
>
> Not sure I understand Daniel's remark about gcc optimization, but the
> change still looks good to me.

Yeah gcc is not clever enought to optimize this away since we can't tell
it that fb->modifier is invariant forever once assigned.
>
> Reviewed-by: Matt Roper <matthew.d.roper@intel.com>

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

Jani, this one is for 4.0-rc.

Thanks, Daniel

>
> > ---
> > drivers/gpu/drm/i915/intel_display.c | 3 ---
> > 1 file changed, 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index 8ccf033..900dcaa 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -12197,9 +12197,6 @@ intel_check_cursor_plane(struct drm_plane *plane,
> > return -ENOMEM;
> > }
> >
> > - if (fb == crtc->cursor->fb)
> > - return 0;
> > -
> > if (fb->modifier[0] != DRM_FORMAT_MOD_NONE) {
> > DRM_DEBUG_KMS("cursor cannot be tiled\n");
> > ret = -EINVAL;
> > --
> > 2.1.0
> >
>
> --
> Matt Roper
> Graphics Software Engineer
> IoTG Platform Enabling & Development
> Intel Corporation
> (916) 356-2795
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch