[PATCH v2 13/21] drm/dp: Do not busy-loop during link training

[Thierry Reding]

From: Thierry Reding <treding at nvidia.com>

Use microsecond sleeps for the clock recovery and channel equalization
delays during link training. The duration of these delays can be from
100 us up to 16 ms. It is rude to busy-loop for that amount of time.

While at it, also convert to standard coding style by putting the
opening braces in a function definition on a new line.

v2: use correct multiplier for training delays (Philipp Zabel)

Signed-off-by: Thierry Reding <treding at nvidia.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 4112570dbe67..681d28988776 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -120,33 +120,39 @@ 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);
 
-void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
-	int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
-			  DP_TRAINING_AUX_RD_MASK;
+void drm_dp_link_train_clock_recovery_delay(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 %d, out of range (max 4)\n",
+		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)
-		udelay(100);
+		rd_interval = 100;
 	else
-		mdelay(rd_interval * 4);
+		rd_interval *= 4 * USEC_PER_MSEC;
+
+	usleep_range(rd_interval, rd_interval * 2);
 }
 EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay);
 
-void drm_dp_link_train_channel_eq_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
-	int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
-			  DP_TRAINING_AUX_RD_MASK;
+void drm_dp_link_train_channel_eq_delay(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 %d, out of range (max 4)\n",
+		DRM_DEBUG_KMS("AUX interval %u, out of range (max 4)\n",
 			      rd_interval);
 
 	if (rd_interval == 0)
-		udelay(400);
+		rd_interval = 400;
 	else
-		mdelay(rd_interval * 4);
+		rd_interval *= 4 * USEC_PER_MSEC;
+
+	usleep_range(rd_interval, rd_interval * 2);
 }
 EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay);
 
-- 
2.22.0