Re: [PATCH] qxl: fix framebuffer unpinning

[Gerd Hoffmann <kraxel@redhat.com>]

On Tue, 2017-09-19 at 11:35 -0300, Gabriel Krisman Bertazi wrote:
> Gerd Hoffmann <kraxel@redhat.com> writes:
> 
> > qxl_plane_cleanup_fb() unpins the just activated framebuffer
> > instead of the old one.  Oops.  Fix it.
> > 
> > Cc: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
> > Fixes: 1277eed5fecb8830c8cc414ad70c1ef640464bc0
> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> > ---
> >  drivers/gpu/drm/qxl/qxl_display.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/qxl/qxl_display.c
> > b/drivers/gpu/drm/qxl/qxl_display.c
> > index e1dd05423e..afbf50d0c0 100644
> > --- a/drivers/gpu/drm/qxl/qxl_display.c
> > +++ b/drivers/gpu/drm/qxl/qxl_display.c
> > @@ -702,14 +702,15 @@ static void qxl_plane_cleanup_fb(struct
> > drm_plane *plane,
> >  	struct drm_gem_object *obj;
> >  	struct qxl_bo *user_bo;
> >  
> > -	if (!plane->state->fb) {
> > -		/* we never executed prepare_fb, so there's
> > nothing to
> > +	if (!old_state->fb) {
> > +		/*
> > +		 * we never executed prepare_fb, so there's
> > nothing to
> >  		 * unpin.
> >  		 */
> >  		return;
> >  	}
> >  
> > -	obj = to_qxl_framebuffer(plane->state->fb)->obj;
> > +	obj = to_qxl_framebuffer(old_state->fb)->obj;
> 
> I am not sure about this patch.  My idea was to pin/unpin the current
> buffer on prepare/cleanup, and only keep it pinned during the atomic
> commit.  This was the goal of 37235451c6990683a8, for instance.

I'm pretty sure the buffer must remain pinned while it is displayed.

> Anyway, if that goal is wrong, I think that, with your change, we
> forget to
> unpin the final plane before removing the device.

"removing the device"?  qxl can't be hotplugged ...
Or do you mean "rmmod qxl"?

cheers,
  Gerd

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