[Intel-gfx] [PATCH v2] drm/i915: Clamp min_cdclk to max_cdclk_freq to unblock 8K

[Manasi Navare]

On Thu, Jul 02, 2020 at 12:15:26PM +0300, Stanislav Lisovskiy wrote:
> We still need "Bump up CDCLK" workaround otherwise getting
> underruns - however currently it blocks 8K as CDCLK = Pixel rate,
> in 8K case would require CDCLK to be around 1 Ghz which is not
> possible.
> 
> v2: - Convert to expression(max(min_cdclk, min(pixel_rate, max_cdclk))
>       (Ville Syrjälä)
>     - Use type specific min_t, max_t(Ville Syrjälä)
> 
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>

I have tested this and this unblocks 8K 

Reviewed-by: Manasi Navare <manasi.d.navare at intel.com>

Manasi

> ---
>  drivers/gpu/drm/i915/display/intel_cdclk.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
> index 45f7f33d1144..8f9320e1e249 100644
> --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> @@ -2080,8 +2080,15 @@ int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state)
>  	 * Explicitly stating here that this seems to be currently
>  	 * rather a Hack, than final solution.
>  	 */
> -	if (IS_TIGERLAKE(dev_priv))
> -		min_cdclk = max(min_cdclk, (int)crtc_state->pixel_rate);
> +	if (IS_TIGERLAKE(dev_priv)) {
> +		/*
> +		 * Clamp to max_cdclk_freq in case pixel rate is higher,
> +		 * in order not to break an 8K, but still leave W/A at place.
> +		 */
> +		min_cdclk = max_t(int, min_cdclk,
> +				  min_t(int, crtc_state->pixel_rate,
> +					dev_priv->max_cdclk_freq));
> +	}
>  
>  	if (min_cdclk > dev_priv->max_cdclk_freq) {
>  		drm_dbg_kms(&dev_priv->drm,
> -- 
> 2.24.1.485.gad05a3d8e5
>