Re: [PATCH] drm/i915/bw: reduce the pm demand peak bw based on display data-rate

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

On Mon, Apr 27, 2026 at 12:11:16PM +0300, Vinod Govindapillai wrote:
> In xe3+, soc can lower the fabric frequency when the display
> needs less bandwidth than the minimum GV point. The threshold
> has been defined as 20GB/s. So if the required display data rate
> is less than this threshold and the slelected GV point is 0 and
> the GV point peak bw is greater than 20GB/s, we could set the
> peak bw for the pm demand to this threshold. The currentc pcode
> can handle this and adjust the fabric frequency accordingly.
> 
> Bspec: 68880
> Signed-off-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_bw.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_bw.c b/drivers/gpu/drm/i915/display/intel_bw.c
> index 9c3a9bbb49f6..005761baca93 100644
> --- a/drivers/gpu/drm/i915/display/intel_bw.c
> +++ b/drivers/gpu/drm/i915/display/intel_bw.c
> @@ -52,6 +52,8 @@ struct intel_qgv_point {
>  
>  #define DEPROGBWPCLIMIT		60
>  
> +#define XE3_PEAK_BW_THRESHOLD	20000
> +
>  struct intel_psf_gv_point {
>  	u8 clk; /* clock in multiples of 16.6666 MHz */
>  };
> @@ -1045,6 +1047,7 @@ static int mtl_find_qgv_points(struct intel_display *display,
>  	unsigned int best_rate = UINT_MAX;
>  	unsigned int num_qgv_points = display->bw.max[0].num_qgv_points;
>  	unsigned int qgv_peak_bw  = 0;
> +	int qgv_point = num_qgv_points;
>  	int i;
>  	int ret;
>  
> @@ -1083,6 +1086,7 @@ static int mtl_find_qgv_points(struct intel_display *display,
>  		if (max_data_rate - data_rate < best_rate) {
>  			best_rate = max_data_rate - data_rate;
>  			qgv_peak_bw = display->bw.max[bw_index].peakbw[i];
> +			qgv_point = i;
>  		}
>  
>  		drm_dbg_kms(display->drm, "QGV point %d: max bw %d required %d qgv_peak_bw: %d\n",
> @@ -1102,6 +1106,18 @@ static int mtl_find_qgv_points(struct intel_display *display,
>  		return -EINVAL;
>  	}
>  
> +	/*
> +	 * For xe3+, if display's required memory bw <= 20GB/s and the selected
> +	 * peak bw of QGV[0] is >= 20 GB/s, we can reduce the peak bw for the
> +	 * pm demand QCLK GV to 20GB/s
> +	 */
> +	if (DISPLAY_VER(display) >= 30 && data_rate <= XE3_PEAK_BW_THRESHOLD &&
> +	    qgv_point == 0 && qgv_peak_bw >= XE3_PEAK_BW_THRESHOLD) {
> +		qgv_peak_bw = XE3_PEAK_BW_THRESHOLD;
> +		drm_dbg_kms(display->drm, "Low display data-rate. Reduce PM demand bw for QGV: %d",
> +			    qgv_peak_bw);
> +	}

I can't figure out what that does. If this is the thing I think it is,
then the plan was to just add a new QGV point (in driver) for the lower
frequency.

> +
>  	/* MTL PM DEMAND expects QGV BW parameter in multiples of 100 mbps */
>  	new_bw_state->qgv_point_peakbw = DIV_ROUND_CLOSEST(qgv_peak_bw, 100);
>  
> -- 
> 2.43.0

-- 
Ville Syrjälä
Intel