Re: [PATCH v2 2/4] drm/vc4: Take underscan setup into account when updating planes

["Ville Syrjälä" <ville.syrjala-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

On Fri, May 11, 2018 at 07:12:21PM +0200, Boris Brezillon wrote:
> On Fri, 11 May 2018 19:54:02 +0300
> Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> 
> > On Fri, May 11, 2018 at 05:52:56PM +0200, Boris Brezillon wrote:
> > > On Fri, 11 May 2018 18:34:50 +0300
> > > Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > >   
> > > > On Fri, May 11, 2018 at 04:59:17PM +0200, Boris Brezillon wrote:  
> > > > > Applying an underscan setup is just a matter of scaling all planes
> > > > > appropriately and adjusting the CRTC X/Y offset to account for the
> > > > > horizontal and vertical border.
> > > > > 
> > > > > Create an vc4_plane_underscan_adj() function doing that and call it from
> > > > > vc4_plane_setup_clipping_and_scaling() so that we are ready to attach
> > > > > underscan properties to the HDMI connector.
> > > > > 
> > > > > Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> > > > > ---
> > > > > Changes in v2:
> > > > > - Take changes on hborder/vborder meaning into account
> > > > > ---
> > > > >  drivers/gpu/drm/vc4/vc4_plane.c | 49 ++++++++++++++++++++++++++++++++++++++++-
> > > > >  1 file changed, 48 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/vc4/vc4_plane.c b/drivers/gpu/drm/vc4/vc4_plane.c
> > > > > index 71d44c357d35..61ed60841cd6 100644
> > > > > --- a/drivers/gpu/drm/vc4/vc4_plane.c
> > > > > +++ b/drivers/gpu/drm/vc4/vc4_plane.c
> > > > > @@ -258,6 +258,49 @@ static u32 vc4_get_scl_field(struct drm_plane_state *state, int plane)
> > > > >  	}
> > > > >  }
> > > > >  
> > > > > +static int vc4_plane_underscan_adj(struct drm_plane_state *pstate)
> > > > > +{
> > > > > +	struct vc4_plane_state *vc4_pstate = to_vc4_plane_state(pstate);
> > > > > +	struct drm_connector_state *conn_state = NULL;
> > > > > +	struct drm_connector *conn;
> > > > > +	struct drm_crtc_state *crtc_state;
> > > > > +	int i;
> > > > > +
> > > > > +	for_each_new_connector_in_state(pstate->state, conn, conn_state, i) {
> > > > > +		if (conn_state->crtc == pstate->crtc)
> > > > > +			break;
> > > > > +	}
> > > > > +
> > > > > +	if (i == pstate->state->num_connector)
> > > > > +		return 0;
> > > > > +
> > > > > +	if (conn_state->underscan.mode != DRM_UNDERSCAN_ON)
> > > > > +		return 0;
> > > > > +
> > > > > +	crtc_state = drm_atomic_get_new_crtc_state(pstate->state,
> > > > > +						   pstate->crtc);
> > > > > +
> > > > > +	if (conn_state->underscan.hborder >= crtc_state->mode.hdisplay ||
> > > > > +	    conn_state->underscan.vborder >= crtc_state->mode.vdisplay)
> > > > > +		return -EINVAL;    
> > > > 
> > > > border * 2 ?  
> > > 
> > > Oops, indeed. I'll fix that.
> > >   
> > > >   
> > > > > +
> > > > > +	vc4_pstate->crtc_x += conn_state->underscan.hborder;
> > > > > +	vc4_pstate->crtc_y += conn_state->underscan.vborder;
> > > > > +	vc4_pstate->crtc_w = (vc4_pstate->crtc_w *
> > > > > +			      (crtc_state->mode.hdisplay -
> > > > > +			       (conn_state->underscan.hborder * 2))) /
> > > > > +			     crtc_state->mode.hdisplay;
> > > > > +	vc4_pstate->crtc_h = (vc4_pstate->crtc_h *
> > > > > +			      (crtc_state->mode.vdisplay -
> > > > > +			       (conn_state->underscan.vborder * 2))) /
> > > > > +			     crtc_state->mode.vdisplay;    
> > > > 
> > > > So you're now scaling all planes? The code seems to reject scaling for
> > > > the cursor plane, how are you dealing with that? Or just no cursor
> > > > allowed when underscanning?  
> > > 
> > > No, I just didn't test with a cursor plane. We should probably avoid
> > > scaling the cursor plane and just adjust its position. Eric any opinion
> > > on that?  
> > 
> > I don't think you can just not scale it. The user asked for the cursor
> > to be at a specific place with a specific size. Can't just ignore
> > that and do something else. Also eg. i915 would definitely scale the
> > cursor since we'd just scale the entire crtc instead of scaling
> > individual planes. Different drivers doing different things wouldn't
> > be good.
> 
> Except in our case the scaling takes place before the composition, so
> we don't have a choice.

The choice is to either do what userspace asked, or return an error.

> 
> > 
> > >   
> > > > 
> > > > I'm also wondering if there's any way we can reconcile these border
> > > > props with the scaling mode prop, should we ever wish to expose
> > > > these props on connectors that already have the scaling mode prop.  
> > > 
> > > Nouveau seems to expose both, and I don't see why we couldn't.  
> > 
> > First of all the interaction of these borders with panels that have
> > a fixed mode would need to be properly specified. Do we apply the
> > borders against the user mode or the panel's native mode?
> 
> Hm, I'm a bit lost. Isn't crtc_state->mode supposed to contain the mode
> that is about to be applied, no matter if it's a usermode or one of the
> mode returned by the display? 

No. With fixed mode panels the user mode is a lie. Only
hdisplay/vdisplay mean anything. The actual timings are known only to
the kernel. Well, userspace can perhaps make an educated guess based on
the connector's mode list and the presence of the scaling mode property.

> 
> > I guess
> > the latter would be a bit easier (would also match how the TV margins
> > behave I suppose). But that does leave open the question of how
> > would generic userspace know which case it's dealing with? Eg. if it
> > wants to underscan by some specific percentage it has to calculate
> > the borders based on the correct mode, otherwise the results aren't
> > going to match the expectations.
> 
> I don't get it, sorry. Borders are relative to the mode applied by
> userspace. So if it needs to express borders as a ratio of the
> resolution, then for sure userspace will have to do the math, but I
> don't see the problem here.

-- 
Ville Syrjälä
Intel
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