From: Thierry Reding <treding@xxxxxxxxxx>
Store the AUX read interval from DPCD, so that it can be used to wait
for the durations given in the specification during link training.
Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
---
include/drm/drm_dp_helper.h | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 7a537ffc2fb1..6c12de6f7e46 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -25,8 +25,11 @@
#include <linux/delay.h>
#include <linux/i2c.h>
+#include <linux/time64.h>
#include <linux/types.h>
+#include <drm/drm_print.h>
+
/*
* Unless otherwise noted, all values are from the DP 1.1a spec. Note that
* DP and DPCD versions are independent. Differences from 1.0 are not noted,
@@ -1297,6 +1300,36 @@ drm_dp_alternate_scrambler_reset_cap(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
DP_ALTERNATE_SCRAMBLER_RESET_CAP;
}
+/**
+ * drm_dp_read_aux_interval() - read the AUX read interval from the DPCD
+ * @dpcd: receiver capacity buffer
+ *
+ * Reads the AUX read interval (in microseconds) from the DPCD. Note that the
+ * TRAINING_AUX_RD_INTERVAL stores the value in units of 4 milliseconds. If no
+ * read interval is specified and for DPCD v1.4 and later, the read interval
+ * is always 100 microseconds.
+ *
+ * Returns:
+ * The read AUX interval in microseconds.
+ */
+static inline unsigned int
+drm_dp_aux_rd_interval(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+ unsigned int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
+ DP_TRAINING_AUX_RD_MASK;
+
+ if (rd_interval > 4)
+ DRM_DEBUG_KMS("AUX interval %u, out of range (max: 4)\n",
+ rd_interval);
+
+ if (rd_interval > 0 && dpcd[DP_DPCD_REV] < DP_DPCD_REV_14)
+ rd_interval *= 4 * USEC_PER_MSEC;
+ else
+ rd_interval = 100;
+
+ return rd_interval;
+}
+
/*
* DisplayPort AUX channel
*/
--
2.23.0
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