[PATCH v5 07/10] drm: Read DP branch device SW revision

[Mika Kahola]

SW revision is mandatory field for DisplayPort branch
devices. This is defined in DPCD register field 0x50A.

Signed-off-by: Mika Kahola <mika.kahola at intel.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 21 +++++++++++++++++++++
 include/drm/drm_dp_helper.h     |  2 ++
 2 files changed, 23 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index b5ae189..80147cd 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -535,6 +535,27 @@ struct drm_dp_revision drm_dp_downstream_hw_rev(struct drm_dp_aux *aux)
 EXPORT_SYMBOL(drm_dp_downstream_hw_rev);
 
 /**
+ * drm_dp_downstream_sw_rev() - read DP branch device SW revision
+ * @aux: DisplayPort AUX channel
+ *
+ * Returns SW revision on success or negative error code on failure
+ */
+struct drm_dp_revision drm_dp_downstream_sw_rev(struct drm_dp_aux *aux)
+{
+	uint8_t tmp[2];
+	struct drm_dp_revision rev = { .major = -EINVAL, .minor = -EINVAL };
+
+	if (drm_dp_dpcd_read(aux, DP_BRANCH_SW_REV, tmp, 2) != 2)
+		return rev;
+
+	rev.major = tmp[0];
+	rev.minor = tmp[1];
+
+	return rev;
+}
+EXPORT_SYMBOL(drm_dp_downstream_sw_rev);
+
+/**
  * drm_dp_downstream_id() - identify branch device
  * @aux: DisplayPort AUX channel
  *
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 641bf3d..c3e4759 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -447,6 +447,7 @@
 #define DP_BRANCH_OUI			    0x500
 #define DP_BRANCH_ID                        0x503
 #define DP_BRANCH_HW_REV                    0x509
+#define DP_BRANCH_SW_REV                    0x50A
 
 #define DP_SET_POWER                        0x600
 # define DP_SET_POWER_D0                    0x1
@@ -819,6 +820,7 @@ int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
 			      const u8 port_cap[4]);
 int drm_dp_downstream_id(struct drm_dp_aux *aux, char id[6]);
 struct drm_dp_revision drm_dp_downstream_hw_rev(struct drm_dp_aux *aux);
+struct drm_dp_revision drm_dp_downstream_sw_rev(struct drm_dp_aux *aux);
 
 int drm_dp_aux_register(struct drm_dp_aux *aux);
 void drm_dp_aux_unregister(struct drm_dp_aux *aux);
-- 
1.9.1