drm/i915/tgl: Clamp min_cdclk to max_cdclk_freq to unblock 8K

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)

Fixes: 46d53e27 ("Revert "drm/i915: Remove unneeded hack now for CDCLK"")
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200702091526.10096-1-stanislav.lisovskiy@intel.com

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,