[PATCH v9 04/12] drm: Helper to read max bits per component

[Mika Kahola]

Helper routine to read out maximum supported bits per
component for DisplayPort legay converters.

v2: Return early if detailed port cap info is not available.
    Replace if-else ladder with switch-case (Ville)

Reviewed-by: Jim Bride <jim.bride at linux.intel.com>
Signed-off-by: Mika Kahola <mika.kahola at intel.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 42 +++++++++++++++++++++++++++++++++++++++++
 include/drm/drm_dp_helper.h     |  2 ++
 2 files changed, 44 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 7497490..14e8ea0 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -472,6 +472,48 @@ int drm_dp_downstream_max_clock(const u8 
dpcd[DP_RECEIVER_CAP_SIZE],
 }
 EXPORT_SYMBOL(drm_dp_downstream_max_clock);

+/**
+ * drm_dp_downstream_max_bpc() - extract branch device max
+ *                               bits per component
+ * @dpcd: DisplayPort configuration data
+ * @port_cap: port capabilities
+ *
+ * Returns max bpc on success or 0 if max bpc not defined
+ */
+int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
+                             const u8 port_cap[4])
+{
+       int type = port_cap[0] & DP_DS_PORT_TYPE_MASK;
+       bool detailed_cap_info = dpcd[DP_DOWNSTREAMPORT_PRESENT] &
+               DP_DETAILED_CAP_INFO_AVAILABLE;
+       int bpc;
+
+       if (!detailed_cap_info)
+               return 0;
+
+       switch (type) {
+       case DP_DS_PORT_TYPE_VGA:
+       case DP_DS_PORT_TYPE_DVI:
+       case DP_DS_PORT_TYPE_HDMI:
+       case DP_DS_PORT_TYPE_DP_DUALMODE:
+               bpc = port_cap[2] & DP_DS_MAX_BPC_MASK;
+
+               switch (bpc) {
+               case DP_DS_8BPC:
+                       return 8;
+               case DP_DS_10BPC:
+                       return 10;
+               case DP_DS_12BPC:
+                       return 12;
+               case DP_DS_16BPC:
+                       return 16;
+               }
+       default:
+               return 0;
+       }
+}
+EXPORT_SYMBOL(drm_dp_downstream_max_bpc);
+
 /*
  * I2C-over-AUX implementation
  */
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 60dd9dc..f3d1424 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -817,6 +817,8 @@ int drm_dp_link_power_down(struct drm_dp_aux *aux, struct 
drm_dp_link *link);
 int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);
 int drm_dp_downstream_max_clock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
                                const u8 port_cap[4]);
+int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
+                             const u8 port_cap[4]);

 void drm_dp_aux_init(struct drm_dp_aux *aux);
 int drm_dp_aux_register(struct drm_dp_aux *aux);
-- 
2.7.4