Re: [PATCH 1/4] drm/i915: Update mbus in intel_dbuf_mbus_update and do it properly

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Mon, Mar 25, 2024 at 04:45:49PM +0200, Ville Syrjälä wrote:
> On Mon, Mar 25, 2024 at 01:23:26PM +0200, Stanislav Lisovskiy wrote:
> > According to BSpec we need to do correspondent MBUS updates before
> > or after DBUF reallocation, depending on whether we are enabling
> > or disabling mbus joining(typical scenario is swithing between
> > multiple and single displays).
> > 
> > Also we need to be able to update dbuf min tracker and mdclk ratio
> > separately if mbus_join state didn't change, so lets add one
> > degree of freedom and make it possible.
> > 
> > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/skl_watermark.c | 54 +++++++++++++-------
> >  1 file changed, 35 insertions(+), 19 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
> > index bc341abcab2fe..2b947870527fc 100644
> > --- a/drivers/gpu/drm/i915/display/skl_watermark.c
> > +++ b/drivers/gpu/drm/i915/display/skl_watermark.c
> > @@ -3570,16 +3570,38 @@ void intel_dbuf_mdclk_cdclk_ratio_update(struct drm_i915_private *i915, u8 ratio
> >  			     DBUF_MIN_TRACKER_STATE_SERVICE(ratio - 1));
> >  }
> >  
> > +static void intel_dbuf_mdclk_min_tracker_update(struct intel_atomic_state *state)
> > +{
> > +	struct drm_i915_private *i915 = to_i915(state->base.dev);
> > +	const struct intel_dbuf_state *old_dbuf_state =
> > +		intel_atomic_get_old_dbuf_state(state);
> > +	const struct intel_dbuf_state *new_dbuf_state =
> > +		intel_atomic_get_new_dbuf_state(state);
> > +
> > +	if (DISPLAY_VER(i915) >= 20 &&
> > +	    old_dbuf_state->mdclk_cdclk_ratio != new_dbuf_state->mdclk_cdclk_ratio) {
> > +		/*
> > +		 * For Xe2LPD and beyond, when there is a change in the ratio
> > +		 * between MDCLK and CDCLK, updates to related registers need to
> > +		 * happen at a specific point in the CDCLK change sequence. In
> > +		 * that case, we defer to the call to
> > +		 * intel_dbuf_mdclk_cdclk_ratio_update() to the CDCLK logic.
> > +		 */
> > +		return;
> > +	}
> 
> That still needs to be removed or else we'll not update the ratio at
> all during the mbus_join changes. I don't think I saw any removal
> in subsequent patches.
> 
> > +
> > +	intel_dbuf_mdclk_cdclk_ratio_update(i915, new_dbuf_state->mdclk_cdclk_ratio,

I don't get what is happening here.

"That whole condition I think needs to go. We want to update the ratio
also when changing mbus joining. But that behavioural change doesn't
really belong in this patch, so this is

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>"

Now it again needs to be changed or changed in other patch(in this series or which one), 
I don't follow.
Should it be the patch changing MBUS join value?

Stan

> 
> And it just occurred to me that this thing will in fact be wrong
> during the pre/post ddb hooks *and* cdclk is getting decreased
> from the post plane update hook.
> 
> I can't immediately think of a super nice way to handle this.
> 
> Perhaps the most stragithforward idea is to just get the mdclk/cdclk
> ratio from i915->display.cdclk.hw during the pre/post ddb hooks.
> cdclk serialization should guard against parallel updates from
> two both places and thus isplay.cdclk.hw should be safe to use.
> 
> The other option would be to determine if a cdclk decrease
> is going to happen or not, and depending on that use the
> old vs. new dbuf_state when updating the ratio in the
> pre/post ddb hooks.
> 
> > +					    new_dbuf_state->joined_mbus);
> > +}
> > +
> >  /*
> >   * Configure MBUS_CTL and all DBUF_CTL_S of each slice to join_mbus state before
> >   * update the request state of all DBUS slices.
> >   */
> > -static void update_mbus_pre_enable(struct intel_atomic_state *state)
> > +static void intel_dbuf_mbus_join_update(struct intel_atomic_state *state)
> >  {
> >  	struct drm_i915_private *i915 = to_i915(state->base.dev);
> >  	u32 mbus_ctl;
> > -	const struct intel_dbuf_state *old_dbuf_state =
> > -		intel_atomic_get_old_dbuf_state(state);
> >  	const struct intel_dbuf_state *new_dbuf_state =
> >  		intel_atomic_get_new_dbuf_state(state);
> >  
> > @@ -3600,21 +3622,6 @@ static void update_mbus_pre_enable(struct intel_atomic_state *state)
> >  	intel_de_rmw(i915, MBUS_CTL,
> >  		     MBUS_HASHING_MODE_MASK | MBUS_JOIN |
> >  		     MBUS_JOIN_PIPE_SELECT_MASK, mbus_ctl);
> > -
> > -	if (DISPLAY_VER(i915) >= 20 &&
> > -	    old_dbuf_state->mdclk_cdclk_ratio != new_dbuf_state->mdclk_cdclk_ratio) {
> > -		/*
> > -		 * For Xe2LPD and beyond, when there is a change in the ratio
> > -		 * between MDCLK and CDCLK, updates to related registers need to
> > -		 * happen at a specific point in the CDCLK change sequence. In
> > -		 * that case, we defer to the call to
> > -		 * intel_dbuf_mdclk_cdclk_ratio_update() to the CDCLK logic.
> > -		 */
> > -		return;
> > -	}
> > -
> > -	intel_dbuf_mdclk_cdclk_ratio_update(i915, new_dbuf_state->mdclk_cdclk_ratio,
> > -					    new_dbuf_state->joined_mbus);
> >  }
> >  
> >  void intel_dbuf_pre_plane_update(struct intel_atomic_state *state)
> > @@ -3632,7 +3639,11 @@ void intel_dbuf_pre_plane_update(struct intel_atomic_state *state)
> >  
> >  	WARN_ON(!new_dbuf_state->base.changed);
> >  
> > -	update_mbus_pre_enable(state);
> > +	if (!old_dbuf_state->joined_mbus && new_dbuf_state->joined_mbus) {
> 
> I think you squashed that stuff into the wrong patch.
> This one should have a pure refactoring patch.
> 
> > +		intel_dbuf_mbus_join_update(state);
> > +		intel_dbuf_mdclk_min_tracker_update(state);
> > +	}
> > +
> >  	gen9_dbuf_slices_update(i915,
> >  				old_dbuf_state->enabled_slices |
> >  				new_dbuf_state->enabled_slices);
> > @@ -3653,6 +3664,11 @@ void intel_dbuf_post_plane_update(struct intel_atomic_state *state)
> >  
> >  	WARN_ON(!new_dbuf_state->base.changed);
> >  
> > +	if (old_dbuf_state->joined_mbus && !new_dbuf_state->joined_mbus) {
> > +		intel_dbuf_mbus_join_update(state);
> > +		intel_dbuf_mdclk_min_tracker_update(state);
> > +	}
> > +
> >  	gen9_dbuf_slices_update(i915,
> >  				new_dbuf_state->enabled_slices);
> >  }
> > -- 
> > 2.37.3
> 
> -- 
> Ville Syrjälä
> Intel