drm/dp: Add drm_dp_dpcd_read_link_status()

The function reads the link status (6 bytes starting at offset 0x202)
from the DPCD so that it can be conveniently passed to other DPCD
helpers.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

2 files changed, 19 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index da6bcfe178a6..84262ed64ce7 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -456,3 +456,19 @@ ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,
                                   size);
 }
 EXPORT_SYMBOL(drm_dp_dpcd_write);
+
+/**
+ * drm_dp_dpcd_read_link_status() - read DPCD link status (bytes 0x202-0x207)
+ * @aux: DisplayPort AUX channel
+ * @status: buffer to store the link status in (must be at least 6 bytes)
+ *
+ * Returns the number of bytes transferred on success or a negative error
+ * code on failure.
+ */
+int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
+                                 u8 status[DP_LINK_STATUS_SIZE])
+{
+        return drm_dp_dpcd_read(aux, DP_LANE0_1_STATUS, status,
+                                DP_LINK_STATUS_SIZE);
+}
+EXPORT_SYMBOL(drm_dp_dpcd_read_link_status);
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 70f18eb3ca1a..a78711feb0d1 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -477,4 +477,7 @@ static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux,
         return drm_dp_dpcd_write(aux, offset, &value, 1);
 }
 
+int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
+                                 u8 status[DP_LINK_STATUS_SIZE]);
+
 #endif /* _DRM_DP_HELPER_H_ */