[RFC v4 16/20] drm/i915/dp: Extract drm_dp_get_sink_count()

[Lyude Paul <lyude@redhat.com>]

And of course, we'll also need to read the sink count from other drivers
as well if we're checking whether or not it's supported. So, let's
extract the code for this into another helper.

v2:
* Fix drm_dp_dpcd_readb() ret check
* Add back comment and move back sink_count assignment in intel_dp_get_dpcd()

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Sean Paul <sean@poorly.run>
---
 drivers/gpu/drm/drm_dp_helper.c         | 22 ++++++++++++++++++++++
 drivers/gpu/drm/i915/display/intel_dp.c | 11 +++++------
 include/drm/drm_dp_helper.h             |  1 +
 3 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 863e0babc1903..67ad05eb05b7e 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -736,6 +736,28 @@ bool drm_dp_has_sink_count(struct drm_connector *connector,
 }
 EXPORT_SYMBOL(drm_dp_has_sink_count);
 
+/**
+ * drm_dp_get_sink_count() - Retrieve the sink count for a given sink
+ * @aux: The DP AUX channel to use
+ *
+ * Returns: The current sink count reported by @aux, or a negative error code
+ * otherwise.
+ */
+int drm_dp_get_sink_count(struct drm_dp_aux *aux)
+{
+	u8 count;
+	int ret;
+
+	ret = drm_dp_dpcd_readb(aux, DP_SINK_COUNT, &count);
+	if (ret < 0)
+		return ret;
+	if (ret != 1)
+		return -EIO;
+
+	return DP_GET_SINK_COUNT(count);
+}
+EXPORT_SYMBOL(drm_dp_get_sink_count);
+
 /*
  * I2C-over-AUX implementation
  */
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 35a4779a442e2..4337321a3be4f 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4648,6 +4648,8 @@ intel_dp_has_sink_count(struct intel_dp *intel_dp)
 static bool
 intel_dp_get_dpcd(struct intel_dp *intel_dp)
 {
+	int ret;
+
 	if (!intel_dp_read_dpcd(intel_dp))
 		return false;
 
@@ -4664,11 +4666,8 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
 	}
 
 	if (intel_dp_has_sink_count(intel_dp)) {
-		u8 count;
-		ssize_t r;
-
-		r = drm_dp_dpcd_readb(&intel_dp->aux, DP_SINK_COUNT, &count);
-		if (r < 1)
+		ret = drm_dp_get_sink_count(&intel_dp->aux);
+		if (ret < 0)
 			return false;
 
 		/*
@@ -4676,7 +4675,7 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
 		 * a member variable in intel_dp will track any changes
 		 * between short pulse interrupts.
 		 */
-		intel_dp->sink_count = DP_GET_SINK_COUNT(count);
+		intel_dp->sink_count = ret;
 
 		/*
 		 * SINK_COUNT == 0 and DOWNSTREAM_PORT_PRESENT == 1 implies that
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index a1413a531eaf4..0c141fc81aaa8 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1635,6 +1635,7 @@ struct drm_dp_desc;
 bool drm_dp_has_sink_count(struct drm_connector *connector,
 			   const u8 dpcd[DP_RECEIVER_CAP_SIZE],
 			   const struct drm_dp_desc *desc);
+int drm_dp_get_sink_count(struct drm_dp_aux *aux);
 
 void drm_dp_remote_aux_init(struct drm_dp_aux *aux);
 void drm_dp_aux_init(struct drm_dp_aux *aux);
-- 
2.26.2