[Intel-gfx] [PATCH] drm/i915: Increase the response time for slow SDVO devices

[Chris Wilson]

Some devices may respond very slowly and only flag that the reply is
pending within the first 15us response window. Be kind to such devices
and wait a further 15ms, before checking for the pending reply. This
moves the existing special case delay of 30ms down from the detection
routine into the common path and pretends to explain it...

Tested-by: bo.b.wang at intel.com
References: https://bugs.freedesktop.org/show_bug.cgi?id=36997
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_sdvo.c |   39 ++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_sdvo.c b/drivers/gpu/drm/i915/intel_sdvo.c
index d85ebb0..f0a1a6f 100644
--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c
@@ -522,19 +522,32 @@ static bool intel_sdvo_read_response(struct intel_sdvo *intel_sdvo,
 	 * command to be complete.
 	 *
 	 * Check 5 times in case the hardware failed to read the docs.
+	 *
+	 * Also beware that the first response by many devices is to
+	 * reply PENDING and stall for time. TVs are notorious for
+	 * requiring longer than specified to complete their replies.
 	 */
 	if (!intel_sdvo_read_byte(intel_sdvo,
 				  SDVO_I2C_CMD_STATUS,
 				  &status))
 		goto log_fail;
 
-	while (status == SDVO_CMD_STATUS_PENDING && retry--) {
-		udelay(15);
-		if (!intel_sdvo_read_byte(intel_sdvo,
-					  SDVO_I2C_CMD_STATUS,
-					  &status))
-			goto log_fail;
-	}
+	do {
+		int quick = 5;
+
+		while (status == SDVO_CMD_STATUS_PENDING && quick--) {
+			udelay(15);
+			if (!intel_sdvo_read_byte(intel_sdvo,
+						  SDVO_I2C_CMD_STATUS,
+						  &status))
+				goto log_fail;
+		}
+
+		if (status != SDVO_CMD_STATUS_PENDING || --retry == 0)
+			break;
+
+		msleep(15);
+	} while (1);
 
 	if (status <= SDVO_CMD_STATUS_SCALING_NOT_SUPP)
 		DRM_LOG_KMS("(%s)", cmd_status_names[status]);
@@ -1535,15 +1548,9 @@ intel_sdvo_detect(struct drm_connector *connector, bool force)
 	struct intel_sdvo_connector *intel_sdvo_connector = to_intel_sdvo_connector(connector);
 	enum drm_connector_status ret;
 
-	if (!intel_sdvo_write_cmd(intel_sdvo,
-				  SDVO_CMD_GET_ATTACHED_DISPLAYS, NULL, 0))
-		return connector_status_unknown;
-
-	/* add 30ms delay when the output type might be TV */
-	if (intel_sdvo->caps.output_flags & SDVO_TV_MASK)
-		msleep(30);
-
-	if (!intel_sdvo_read_response(intel_sdvo, &response, 2))
+	if (!intel_sdvo_get_value(intel_sdvo,
+				  SDVO_CMD_GET_ATTACHED_DISPLAYS,
+				  &response, 2))
 		return connector_status_unknown;
 
 	DRM_DEBUG_KMS("SDVO response %d %d [%x]\n",
-- 
1.7.10.4