linux-kernel - [PATCH v2 3/8] drm: zynqmp_dp: Adjust training values per-lane

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Message-Id: <20240319225122.3048400-4-sean.anderson@linux.dev>
Date: Tue, 19 Mar 2024 18:51:16 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	dri-devel@...ts.freedesktop.org
Cc: Michal Simek <michal.simek@....com>,
	David Airlie <airlied@...il.com>,
	linux-kernel@...r.kernel.org,
	Daniel Vetter <daniel@...ll.ch>,
	linux-arm-kernel@...ts.infradead.org,
	Sean Anderson <sean.anderson@...ux.dev>
Subject: [PATCH v2 3/8] drm: zynqmp_dp: Adjust training values per-lane

The feedback we get from the DPRX is per-lane. Make changes using this
information, instead of picking the maximum values from all lanes. This
results in more-consistent training on marginal links.

Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
---

(no changes since v1)

 drivers/gpu/drm/xlnx/zynqmp_dp.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
index 98a32e6a0459..8635b5673386 100644
--- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
+++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
@@ -605,28 +605,21 @@ static void zynqmp_dp_adjust_train(struct zynqmp_dp *dp,
 				   u8 link_status[DP_LINK_STATUS_SIZE])
 {
 	u8 *train_set = dp->train_set;
-	u8 voltage = 0, preemphasis = 0;
 	u8 i;
 
 	for (i = 0; i < dp->mode.lane_cnt; i++) {
-		u8 v = drm_dp_get_adjust_request_voltage(link_status, i);
-		u8 p = drm_dp_get_adjust_request_pre_emphasis(link_status, i);
+		u8 voltage = drm_dp_get_adjust_request_voltage(link_status, i);
+		u8 preemphasis =
+			drm_dp_get_adjust_request_pre_emphasis(link_status, i);
 
-		if (v > voltage)
-			voltage = v;
+		if (voltage >= DP_TRAIN_VOLTAGE_SWING_LEVEL_3)
+			voltage |= DP_TRAIN_MAX_SWING_REACHED;
 
-		if (p > preemphasis)
-			preemphasis = p;
-	}
+		if (preemphasis >= DP_TRAIN_PRE_EMPH_LEVEL_2)
+			preemphasis |= DP_TRAIN_MAX_PRE_EMPHASIS_REACHED;
 
-	if (voltage >= DP_TRAIN_VOLTAGE_SWING_LEVEL_3)
-		voltage |= DP_TRAIN_MAX_SWING_REACHED;
-
-	if (preemphasis >= DP_TRAIN_PRE_EMPH_LEVEL_2)
-		preemphasis |= DP_TRAIN_MAX_PRE_EMPHASIS_REACHED;
-
-	for (i = 0; i < dp->mode.lane_cnt; i++)
 		train_set[i] = voltage | preemphasis;
+	}
 }
 
 /**
-- 
2.35.1.1320.gc452695387.dirty