[PATCH v2 05/14] drm/i915: Avoid triggering unwanted cdclk changes due to dbuf bandwidth changes

[Jani Nikula]

On Wed, 26 Mar 2025, Ville Syrjala <ville.syrjala at linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>
> Currently intel_bw_calc_min_cdclk() always adds the bw_state
> to the atomic state. Not only does it result in potentially
> redundant work later, it's also currently causing unwanted cdclk
> changes during driver load.

Can you elaborate how we currently end up changing cdclk even if the
dbuf bw isn't changing? Different rules wrt to GOP?

Anyway, the change make sense no matter what,

Reviewed-by: Jani Nikula <jani.nikula at intel.com>


>
> Check if the dbuf bw is actually changing before we decide to
> pull in the bw state.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_bw.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_bw.c b/drivers/gpu/drm/i915/display/intel_bw.c
> index 67d088da1f38..19b516084fac 100644
> --- a/drivers/gpu/drm/i915/display/intel_bw.c
> +++ b/drivers/gpu/drm/i915/display/intel_bw.c
> @@ -1294,7 +1294,8 @@ int intel_bw_calc_min_cdclk(struct intel_atomic_state *state,
>  	struct intel_bw_state *new_bw_state = NULL;
>  	const struct intel_bw_state *old_bw_state = NULL;
>  	const struct intel_cdclk_state *cdclk_state;
> -	const struct intel_crtc_state *crtc_state;
> +	const struct intel_crtc_state *old_crtc_state;
> +	const struct intel_crtc_state *new_crtc_state;
>  	int old_min_cdclk, new_min_cdclk;
>  	struct intel_crtc *crtc;
>  	int i;
> @@ -1302,15 +1303,23 @@ int intel_bw_calc_min_cdclk(struct intel_atomic_state *state,
>  	if (DISPLAY_VER(display) < 9)
>  		return 0;
>  
> -	for_each_new_intel_crtc_in_state(state, crtc, crtc_state, i) {
> +	for_each_oldnew_intel_crtc_in_state(state, crtc, old_crtc_state,
> +					    new_crtc_state, i) {
> +		struct intel_dbuf_bw old_dbuf_bw, new_dbuf_bw;
> +
> +		skl_crtc_calc_dbuf_bw(&old_dbuf_bw, old_crtc_state);
> +		skl_crtc_calc_dbuf_bw(&new_dbuf_bw, new_crtc_state);
> +
> +		if (!intel_dbuf_bw_changed(display, &old_dbuf_bw, &new_dbuf_bw))
> +			continue;
> +
>  		new_bw_state = intel_atomic_get_bw_state(state);
>  		if (IS_ERR(new_bw_state))
>  			return PTR_ERR(new_bw_state);
>  
>  		old_bw_state = intel_atomic_get_old_bw_state(state);
>  
> -		skl_crtc_calc_dbuf_bw(&new_bw_state->dbuf_bw[crtc->pipe],
> -				      crtc_state);
> +		new_bw_state->dbuf_bw[crtc->pipe] = new_dbuf_bw;
>  	}
>  
>  	if (!old_bw_state)

-- 
Jani Nikula, Intel