Re: [PATCH 3/7] drm/vmwgfx: Stop using plane->fb in vmw_kms_helper_dirty()

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Apr 05, 2018 at 10:15:57PM +0200, Thomas Hellstrom wrote:
> On 04/05/2018 09:50 PM, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Instead of plane->fb (which we're going to deprecate for atomic drivers)
> > we need to look at plane->state->fb. The maze of code leading to
> > vmw_kms_helper_dirty() wasn't particularly clear, but my analysis
> > concluded that the calls originating from vmw_*_primary_plane_atomic_update()
> > all pass in the crtc which means we'll never end up in this branch
> > of the function. All other callers use drm_modeset_lock_all() somewhere
> > higher up, which means accessing plane->state is safe. We'll toss in
> > a lockdep assert to catch wrongdoers.
> >
> > Cc: Thomas Hellstrom <thellstrom@vmware.com>
> > Cc: Sinclair Yeh <syeh@vmware.com>
> > Cc: VMware Graphics <linux-graphics-maintainer@vmware.com>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >   drivers/gpu/drm/vmwgfx/vmwgfx_kms.c | 15 ++++++++++++---
> >   1 file changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> > index a2a796b4cc23..5a824125c231 100644
> > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> > @@ -2326,9 +2326,18 @@ int vmw_kms_helper_dirty(struct vmw_private *dev_priv,
> >   	} else {
> >   		list_for_each_entry(crtc, &dev_priv->dev->mode_config.crtc_list,
> >   				    head) {
> > -			if (crtc->primary->fb != &framebuffer->base)
> > -				continue;
> > -			units[num_units++] = vmw_crtc_to_du(crtc);
> > +			struct drm_plane *plane = crtc->primary;
> > +
> > +			/*
> > +			 * vmw_*_primary_plane_atomic_update() pass in the crtc,
> > +			 * and so don't end up here. All other callers use
> > +			 * drm_modeset_lock_all(), hence we can access the
> > +			 * plane state safely.
> > +			 */
> > +			lockdep_assert_held(&plane->mutex);
> > +
> I think we can remove the comment (it's a helper, so current users may 
> not be future users),
> but the lockdep assert should be OK.

OK.

> > +			if (plane->state->fb != &framebuffer->base)
> > +				units[num_units++] = vmw_crtc_to_du(crtc);
> 
> This doesn't seem to do what the original code did...

Whoops. Good catch.

> 
> >   		}
> >   	}
> >   
> 
> /Thomas
> 

-- 
Ville Syrjälä
Intel OTC
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