drm/dp: add DP 2.0 UHBR link rate and bw code conversions

The bw code equals link_rate / 0.27 Gbps only for 8b/10b link
rates. Handle DP 2.0 UHBR rates as special cases, though this is not
pretty.

Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/cab4edda8834d6b4db610fabb5e1f1f18ae33c2c.1631191763.git.jani.nikula@intel.com

drivers/gpu/drm/drm_dp_helper.c

@@ -207,15 +207,33 @@ EXPORT_SYMBOL(drm_dp_lttpr_link_train_channel_eq_delay);
 
 u8 drm_dp_link_rate_to_bw_code(int link_rate)
 {
-	/* Spec says link_bw = link_rate / 0.27Gbps */
-	return link_rate / 27000;
+	switch (link_rate) {
+	case 1000000:
+		return DP_LINK_BW_10;
+	case 1350000:
+		return DP_LINK_BW_13_5;
+	case 2000000:
+		return DP_LINK_BW_20;
+	default:
+		/* Spec says link_bw = link_rate / 0.27Gbps */
+		return link_rate / 27000;
+	}
 }
 EXPORT_SYMBOL(drm_dp_link_rate_to_bw_code);
 
 int drm_dp_bw_code_to_link_rate(u8 link_bw)
 {
-	/* Spec says link_rate = link_bw * 0.27Gbps */
-	return link_bw * 27000;
+	switch (link_bw) {
+	case DP_LINK_BW_10:
+		return 1000000;
+	case DP_LINK_BW_13_5:
+		return 1350000;
+	case DP_LINK_BW_20:
+		return 2000000;
+	default:
+		/* Spec says link_rate = link_bw * 0.27Gbps */
+		return link_bw * 27000;
+	}
 }
 EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate);