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 07:11:21PM +0200, Ville Syrjälä wrote:
> On Mon, Mar 25, 2024 at 07:01:03PM +0200, Lisovskiy, Stanislav wrote:
> > 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?
> 
> Yeah, probably should be in the last patch. Perhaps we
> could change it before that, but that would need some
> extra brain power to make sure it doesn't temporarily
> break something. So probably not worth the hassle
> to do as a separate patch.
> 
> > 
> > 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.

First of all why that
condition above prevents update when mbus join changes?
It exits when mdclk_cdclk ratio is changed not mbus_join?

That review process to me seems rather chaotic.
Constantly something new pops up, moreover we did previously agree
about that code.

> > > 
> > > 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
> 
> -- 
> Ville Syrjälä
> Intel