[RFC 08/13] drm/dp: Add helper to get post-cursor adjustments

[Thierry Reding <thierry.reding@gmail.com>]

From: Thierry Reding <treding@nvidia.com>

If the transmitter supports pre-emphasis post cursor2 the sink will
request adjustments in a similar way to how it requests adjustments to
the voltage swing and pre-emphasis settings.

Add a helper to extract these adjustments on a per-lane basis from the
DPCD link status.

Signed-off-by: Thierry Reding <treding@nvidia.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 10 ++++++++++
 include/drm/drm_dp_helper.h     | 12 ++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 9d6ef0576abc..d503cc3f1772 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -115,6 +115,16 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SI
 }
 EXPORT_SYMBOL(drm_dp_get_adjust_request_pre_emphasis);
 
+u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],
+					 unsigned int lane)
+{
+	unsigned int offset = DP_ADJUST_REQUEST_POST_CURSOR2;
+	u8 value = dp_link_status(link_status, offset);
+
+	return (value >> (lane << 1)) & 0x3;
+}
+EXPORT_SYMBOL(drm_dp_get_adjust_request_post_cursor);
+
 void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
 	if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
 		udelay(100);
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 1fda4643af1f..2165b9ef8504 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -400,6 +400,16 @@
 # define DP_ADJUST_PRE_EMPHASIS_LANE1_MASK   0xc0
 # define DP_ADJUST_PRE_EMPHASIS_LANE1_SHIFT  6
 
+#define DP_ADJUST_REQUEST_POST_CURSOR2	    0x20c
+# define DP_ADJUST_POST_CURSOR2_LANE0_MASK  0x03
+# define DP_ADJUST_POST_CURSOR2_LANE0_SHIFT 0
+# define DP_ADJUST_POST_CURSOR2_LANE1_MASK  0x0c
+# define DP_ADJUST_POST_CURSOR2_LANE1_SHIFT 2
+# define DP_ADJUST_POST_CURSOR2_LANE2_MASK  0x30
+# define DP_ADJUST_POST_CURSOR2_LANE2_SHIFT 4
+# define DP_ADJUST_POST_CURSOR2_LANE3_MASK  0xc0
+# define DP_ADJUST_POST_CURSOR2_LANE3_SHIFT 6
+
 #define DP_TEST_REQUEST			    0x218
 # define DP_TEST_LINK_TRAINING		    (1 << 0)
 # define DP_TEST_LINK_VIDEO_PATTERN	    (1 << 1)
@@ -578,6 +588,8 @@ u8 drm_dp_get_adjust_request_voltage(const u8 link_status[DP_LINK_STATUS_SIZE],
 				     int lane);
 u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SIZE],
 					  int lane);
+u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],
+					 unsigned int lane);
 
 #define DP_RECEIVER_CAP_SIZE		0xf
 #define EDP_PSR_RECEIVER_CAP_SIZE	2
-- 
2.4.5

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