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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

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,

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