[Intel-gfx] [PATCH] drm/i915/adl_p: Increase CDCLK by 15% if PSR2 is used

[Souza, Jose]

On Fri, 2022-03-18 at 10:52 +0200, Stanislav Lisovskiy wrote:
> We are currently getting FIFO underruns, in particular
> when PSR2 is enabled. There seem to be no existing workaround
> or patches, which can fix that issue(were expecting some recent
> selective fetch update and DBuf bw/SAGV fixes to help,
> which unfortunately didn't).
> Current idea is that it looks like for some reason the
> DBuf prefill time isn't enough once we exit PSR2, despite its
> theoretically correct.
> So bump it up a bit by 15%(minimum experimental amount required
> to get it working), if PSR2 is enabled.
> For PSR1 there is no need in this hack, so we limit it only
> to PSR2 and Alderlake.

It this workaround meant to be permanent? If yes we should file a HSD and get hardware folks feedback.

> 
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_cdclk.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
> index 8888fda8b701..095b79950788 100644
> --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> @@ -2325,6 +2325,19 @@ int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state)
>  					dev_priv->max_cdclk_freq));
>  	}
>  

Please add some comment in the code about this workaround.


> +	if (IS_ALDERLAKE_P(dev_priv)) {
> +		struct intel_encoder *encoder;
> +
> +		for_each_intel_encoder_with_psr(&dev_priv->drm, encoder) {
> +			struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
> +
> +			if (intel_dp->psr.psr2_enabled) {

You should check the has_psr2 in the crtc_state, PSR2 could be disabled when this state is committed.

> +				min_cdclk = DIV_ROUND_UP(min_cdclk * 100, 85);

This is not increasing by 15%.

min_cdclk = 500
500 * 100 = 50000
50000 / 85 = 588.235294118

While 15% of 500 is 75.

Also if there is two CRTCs with PSR2 enabled you will bump min_cdclk twice.

> +				break;
> +			}
> +		}
> +	}
> +
>  	if (min_cdclk > dev_priv->max_cdclk_freq) {
>  		drm_dbg_kms(&dev_priv->drm,
>  			    "required cdclk (%d kHz) exceeds max (%d kHz)\n",