[PATCH 2/4] drm/i915: Break intel_dbuf_mbus_update into 2 separate parts

[Lisovskiy, Stanislav]

On Mon, Mar 18, 2024 at 08:01:41PM +0200, Ville Syrjälä wrote:
> On Sun, Mar 17, 2024 at 07:24:14PM +0200, Stanislav Lisovskiy wrote:
> > 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.
> > 
> > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/skl_watermark.c | 55 ++++++++++++--------
> >  1 file changed, 33 insertions(+), 22 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
> > index 2d3b08c2f8d78..d7d2278fd201c 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;
> > +	}
> > +
> > +	intel_dbuf_mdclk_cdclk_ratio_update(i915, new_dbuf_state->mdclk_cdclk_ratio,
> > +					    new_dbuf_state->joined_mbus);
> > +}
> 
> Argh. The hardware is turning into a disaster with all these
> links between different units.
> 
> This whole thing looks rather suspicious as the cdclk changes
> and mbus joining changes don't happen in sync.
> 
> AFAICS the sequence should end up doing more or less like this:
> 1. disable pipes
> 2. increase cdclk
>   2.1 reprogram cdclk
>   2.2 update dbuf tracker value
> 3. enable mbus joining if necessary
>  3.1 update mbus_ctl
>  3.2 update dbuf tracker value
> 4. reallocate dbuf for planes on active pipes
> 5. disable mbus joining if necessary
>  5.1 update dbuf tracker value
>  5.2 update mbus_ctl
> 6. enable pipes
> 7. decrease cdclk, mbus joining is unchanged
>   7.1 update dbuf tracker value
>   7.2 reprogram cdclk
> 
> So step 2.2 should keep using the old mbus_join valued when
> updating the ratio, and steps 3.2,5.1,7.1 should use the new
> value. That's assuming there is actually some ordering
> requirements between these steps (whch bspec does seem to
> imply).

So does it mean, we are missing updating dbuf tracker value
in CDCLK programming path?

Stan

> 
> -- 
> Ville Syrjälä
> Intel