[PATCH 9/9] Revert "drm/i915/xe2lpd: Treat cursor plane as regular plane for DDB allocation"

[Ville Syrjälä]

On Wed, Dec 13, 2023 at 01:28:15PM +0200, Lisovskiy, Stanislav wrote:
> On Wed, Dec 13, 2023 at 12:25:19PM +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > This reverts commit cfeff354f70bb1d0deb0279506e3f7989bc16e28.
> > 
> > A core design consideration with legacy cursor updates is that the
> > cursor must not touch any other plane, even if we were to force it
> > to take the slow path. That is the real reason why the cursor uses
> > a fixed ddb allocation, not because bspec says so.
> > 
> > Treating cursors as any other plane during ddb allocation
> > violates that, which means we can now pull other planes into
> > fully unsynced legacy cursor mailbox commits. That is
> > definitely not something we've ever considered when designing
> > the rest of the code. The noarm+arm register write split in
> > particular makes that dangerous as previous updates can get
> > disarmed pretty much at any random time, and not necessarily
> > in an order that is actually safe (eg. against ddb overlaps).
> > 
> > So if we were to do this then:
> > - someone needs to expend the appropriate amount of brain
> >   cells thinking through all the tricky details
> 
> So question is how can we avoid pulling other planes to the commit?..

By preallocating the ddb, as we do already.

> 
> 
> Stan
> 
> > - we should do it for all skl+ platforms since all
> >   of those have double buffered wm/ddb registers. The current
> >   arbitrary mtl+ cutoff doesn't really make sense
> > 
> > For the moment just go back to the original behaviour where
> > the cursor's ddb alloation does not change outside of
> > modeset/fastset. As of now anything else isn't safe.
> > 
> > Cc: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> > Cc: Matt Roper <matthew.d.roper at intel.com>
> > Cc: Lucas De Marchi <lucas.demarchi at intel.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > ---
> >  .../gpu/drm/i915/display/intel_atomic_plane.c    |  6 +++---
> >  drivers/gpu/drm/i915/display/skl_watermark.c     | 16 +++++++---------
> >  2 files changed, 10 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_atomic_plane.c b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> > index 06c2455bdd78..76d77d5a0409 100644
> > --- a/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> > +++ b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> > @@ -217,6 +217,9 @@ intel_plane_relative_data_rate(const struct intel_crtc_state *crtc_state,
> >  	int width, height;
> >  	unsigned int rel_data_rate;
> >  
> > +	if (plane->id == PLANE_CURSOR)
> > +		return 0;
> > +
> >  	if (!plane_state->uapi.visible)
> >  		return 0;
> >  
> > @@ -244,9 +247,6 @@ intel_plane_relative_data_rate(const struct intel_crtc_state *crtc_state,
> >  
> >  	rel_data_rate = width * height * fb->format->cpp[color_plane];
> >  
> > -	if (plane->id == PLANE_CURSOR)
> > -		return rel_data_rate;
> > -
> >  	return intel_adjusted_rate(&plane_state->uapi.src,
> >  				   &plane_state->uapi.dst,
> >  				   rel_data_rate);
> > diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
> > index 56588d6e24ae..051a02ac01a4 100644
> > --- a/drivers/gpu/drm/i915/display/skl_watermark.c
> > +++ b/drivers/gpu/drm/i915/display/skl_watermark.c
> > @@ -1367,7 +1367,7 @@ skl_total_relative_data_rate(const struct intel_crtc_state *crtc_state)
> >  	u64 data_rate = 0;
> >  
> >  	for_each_plane_id_on_crtc(crtc, plane_id) {
> > -		if (plane_id == PLANE_CURSOR && DISPLAY_VER(i915) < 20)
> > +		if (plane_id == PLANE_CURSOR)
> >  			continue;
> >  
> >  		data_rate += crtc_state->rel_data_rate[plane_id];
> > @@ -1514,12 +1514,10 @@ skl_crtc_allocate_plane_ddb(struct intel_atomic_state *state,
> >  		return 0;
> >  
> >  	/* Allocate fixed number of blocks for cursor. */
> > -	if (DISPLAY_VER(i915) < 20) {
> > -		cursor_size = skl_cursor_allocation(crtc_state, num_active);
> > -		iter.size -= cursor_size;
> > -		skl_ddb_entry_init(&crtc_state->wm.skl.plane_ddb[PLANE_CURSOR],
> > -				   alloc->end - cursor_size, alloc->end);
> > -	}
> > +	cursor_size = skl_cursor_allocation(crtc_state, num_active);
> > +	iter.size -= cursor_size;
> > +	skl_ddb_entry_init(&crtc_state->wm.skl.plane_ddb[PLANE_CURSOR],
> > +			   alloc->end - cursor_size, alloc->end);
> >  
> >  	iter.data_rate = skl_total_relative_data_rate(crtc_state);
> >  
> > @@ -1533,7 +1531,7 @@ skl_crtc_allocate_plane_ddb(struct intel_atomic_state *state,
> >  			const struct skl_plane_wm *wm =
> >  				&crtc_state->wm.skl.optimal.planes[plane_id];
> >  
> > -			if (plane_id == PLANE_CURSOR && DISPLAY_VER(i915) < 20) {
> > +			if (plane_id == PLANE_CURSOR) {
> >  				const struct skl_ddb_entry *ddb =
> >  					&crtc_state->wm.skl.plane_ddb[plane_id];
> >  
> > @@ -1581,7 +1579,7 @@ skl_crtc_allocate_plane_ddb(struct intel_atomic_state *state,
> >  		const struct skl_plane_wm *wm =
> >  			&crtc_state->wm.skl.optimal.planes[plane_id];
> >  
> > -		if (plane_id == PLANE_CURSOR && DISPLAY_VER(i915) < 20)
> > +		if (plane_id == PLANE_CURSOR)
> >  			continue;
> >  
> >  		if (DISPLAY_VER(i915) < 11 &&
> > -- 
> > 2.41.0
> > 

-- 
Ville Syrjälä
Intel