[Intel-gfx] [PATCH 2/2] drm/i915: add module param for live_status

[David Weinehall]

Since the workaround for buggy displays that do not reply to
live status detect immediately affects a rather limited set of
displays, and since the price paid (almost 100ms per HDMI-port),
we should have that hack disabled by default.

Rather than leaving people with these kinds of broken displays
out in the cold completely, add a module parameter, defaulting
to -1 (live status detection on supported platforms, but without
the extra delays), that allows for re-enabling this hack.

Signed-off-by: David Weinehall <david.weinehall at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_params.c |  8 ++++++++
 drivers/gpu/drm/i915/i915_params.h |  1 +
 drivers/gpu/drm/i915/intel_hdmi.c  | 20 ++++++++++++++++++--
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index 768ad89d9cd4..ad5988b17656 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/drivers/gpu/drm/i915/i915_params.c
@@ -62,6 +62,7 @@ struct i915_params i915 __read_mostly = {
 	.inject_load_failure = 0,
 	.enable_dpcd_backlight = false,
 	.enable_gvt = false,
+	.live_status = -1,
 };
 
 module_param_named(modeset, i915.modeset, int, 0400);
@@ -233,3 +234,10 @@ MODULE_PARM_DESC(enable_dpcd_backlight,
 module_param_named(enable_gvt, i915.enable_gvt, bool, 0400);
 MODULE_PARM_DESC(enable_gvt,
 	"Enable support for Intel GVT-g graphics virtualization host support(default:false)");
+
+module_param_named(live_status, i915.live_status, int, 0600);
+MODULE_PARM_DESC(live_status,
+	"Enable live status detection "
+	"(-1=auto [default], "
+	  "0=disabled, "
+	  "1=enabled with extra delay)");
diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
index 3a0dd78ddb38..2ff2083936e3 100644
--- a/drivers/gpu/drm/i915/i915_params.h
+++ b/drivers/gpu/drm/i915/i915_params.h
@@ -52,6 +52,7 @@ struct i915_params {
 	int mmio_debug;
 	int edp_vswing;
 	unsigned int inject_load_failure;
+	int live_status;
 	/* leave bools at the end to not create holes */
 	bool enable_hangcheck;
 	bool fastboot;
diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
index 713c91ce7f70..b7d88728335a 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -1468,6 +1468,7 @@ intel_hdmi_detect(struct drm_connector *connector, bool force)
 	struct intel_hdmi *intel_hdmi = intel_attached_hdmi(connector);
 	struct drm_i915_private *dev_priv = to_i915(connector->dev);
 	bool live_status = false;
+	int attempts = 1;
 	unsigned int try;
 
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n",
@@ -1478,12 +1479,27 @@ intel_hdmi_detect(struct drm_connector *connector, bool force)
 	/*
 	 * Live status register is not reliable on all intel platforms.
 	 * So consider live_status only for certain platforms, for
-	 * others, read EDID to determine presence of sink.
+	 * others, read EDID to determine presence of sink, unless
+	 * the users explicitly disables live status reads. For users
+	 * who have broken displays we offer the option to use
+	 * live status with an extra delay.
 	 */
+	switch (i915.live_status) {
+	case 0:
+		live_status = true;
+		break;
+	case 1:
+		attempts = 9;
+		break;
+	default:
+	case -1:
+		break;
+	}
+
 	if (INTEL_INFO(dev_priv)->gen < 7 || IS_IVYBRIDGE(dev_priv))
 		live_status = true;
 
-	for (try = 0; !live_status && try < 9; try++) {
+	for (try = 0; !live_status && try < attempts; try++) {
 		if (try)
 			msleep(10);
 		live_status = intel_digital_port_connected(dev_priv,
-- 
2.8.1