[Intel-gfx] [PATCH 2/4] drm/i915: Don't check for wm changes until we've compute the wms fully

[Souza, Jose]

On Fri, 2020-02-28 at 22:35 +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Currently we're comparing the watermarks between the old and new
> states
> before we've fully computed the new watermarks. In particular
> skl_build_pipe_wm() will not account for the amount of ddb space
> we'll
> have. That information is only available during skl_compute_ddb()
> which will proceed to zero out any watermark level exceeding the
> ddb allocation. If we're short on ddb space this will end up
> adding the plane to the state due erronously determining that the
> watermarks have changed. Fix the problem by deferring
> skl_wm_add_affected_planes() until we have the final watermarks
> computed.
> 
> Noticed this when trying enable transition watermarks on glk.
> We now computed the trans_wm as 28, but we only had 14 blocks
> of ddb, and thus skl_compute_ddb() ended up disabling the cursor
> trans_wm every time. Thus we ended up adding the cursor to every
> commit that didn't actually affect the cursor at all.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c
> b/drivers/gpu/drm/i915/intel_pm.c
> index 39299811b650..a3d76e69caae 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -5762,16 +5762,24 @@ skl_compute_wm(struct intel_atomic_state
> *state)
>  		ret = skl_build_pipe_wm(new_crtc_state);
>  		if (ret)
>  			return ret;
> -
> -		ret = skl_wm_add_affected_planes(state, crtc);
> -		if (ret)
> -			return ret;
>  	}
>  
>  	ret = skl_compute_ddb(state);
>  	if (ret)
>  		return ret;
>  
> +	/*
> +	 * skl_compute_ddb() will have adjusted the final watermarks
> +	 * based on how much ddb is available. Now we can actually
> +	 * check if the final watermarks changed.
> +	 */
> +	for_each_oldnew_intel_crtc_in_state(state, crtc,
> old_crtc_state,
> +					    new_crtc_state, i) {
> +		ret = skl_wm_add_affected_planes(state, crtc);
> +		if (ret)
> +			return ret;
> +	}

skl_compute_ddb() is already calling skl_wm_add_affected_planes() after
do the ddb allocation for each pipe, so we could remove this chunk,
with that:

Reviewed-by: José Roberto de Souza <jose.souza at intel.com>

> +
>  	skl_print_wm_changes(state);
>  
>  	return 0;