[PATCH v4 08/11] drm: Read DP branch device SW revision

[Mika Kahola <mika.kahola@xxxxxxxxx>]

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

Signed-off-by: Mika Kahola <mika.kahola@xxxxxxxxx>
---
 drivers/gpu/drm/drm_dp_helper.c | 22 ++++++++++++++++++++++
 include/drm/drm_dp_helper.h     |  4 +++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 6dd9ff5..89b3b24 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -571,6 +571,28 @@ 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);
+
 /*
  * I2C-over-AUX implementation
  */
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 08a10b3..1848320 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
@@ -823,7 +824,8 @@ 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

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