[ 3.8.y.z extended stable ] Patch "Partially revert "drm/i915: unconditionally use mt forcewake on" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    Partially revert "drm/i915: unconditionally use mt forcewake on

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.6.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 5ce34926a10cb5be0fd2e1817ccc116817ec640f Mon Sep 17 00:00:00 2001
From: Guenter Roeck <linux at roeck-us.net>
Date: Tue, 9 Jul 2013 16:00:31 -0700
Subject: Partially revert "drm/i915: unconditionally use mt forcewake on
 hsw/ivb"

commit c11e5f35ab490bd30591563816fbc83526521777 upstream.

This patch partially reverts commit 36ec8f877481449bdfa072e6adf2060869e2b970 for
IvyBridge CPUs.

The original commit results in repeated 'Timed out waiting for forcewake old
ack to clear' messages on a Supermicro C7H61 board (BIOS version 2.00 and 2.00b)
with i7-3770K CPU. It ultimately results in a hangup if the system is highly
loaded. Reverting the commit for IvyBridge CPUs fixes the issue.

Issue a warning if the CPU is IvyBridge and mt forcewake is disabled, since
this condition can result in secondary issues.

v2: Only revert patch for Ivybridge CPUs
    Issue info message if mt forcewake is disabled on Ivybridge

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=60541
Cc: Jesse Barnes <jbarnes at virtuousgeek.org>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
Signed-off-by: Guenter Roeck <linux at roeck-us.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=66139
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 253bcf3..e8c7ade 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -4411,9 +4411,38 @@ void intel_gt_init(struct drm_device *dev)
 	if (IS_VALLEYVIEW(dev)) {
 		dev_priv->gt.force_wake_get = vlv_force_wake_get;
 		dev_priv->gt.force_wake_put = vlv_force_wake_put;
-	} else if (IS_IVYBRIDGE(dev) || IS_HASWELL(dev)) {
+	} else if (IS_HASWELL(dev)) {
 		dev_priv->gt.force_wake_get = __gen6_gt_force_wake_mt_get;
 		dev_priv->gt.force_wake_put = __gen6_gt_force_wake_mt_put;
+	} else if (IS_IVYBRIDGE(dev)) {
+		u32 ecobus;
+
+		/* IVB configs may use multi-threaded forcewake */
+
+		/* A small trick here - if the bios hasn't configured
+		 * MT forcewake, and if the device is in RC6, then
+		 * force_wake_mt_get will not wake the device and the
+		 * ECOBUS read will return zero. Which will be
+		 * (correctly) interpreted by the test below as MT
+		 * forcewake being disabled.
+		 */
+		mutex_lock(&dev->struct_mutex);
+		__gen6_gt_force_wake_mt_get(dev_priv);
+		ecobus = I915_READ_NOTRACE(ECOBUS);
+		__gen6_gt_force_wake_mt_put(dev_priv);
+		mutex_unlock(&dev->struct_mutex);
+
+		if (ecobus & FORCEWAKE_MT_ENABLE) {
+			dev_priv->gt.force_wake_get =
+						__gen6_gt_force_wake_mt_get;
+			dev_priv->gt.force_wake_put =
+						__gen6_gt_force_wake_mt_put;
+		} else {
+			DRM_INFO("No MT forcewake available on Ivybridge, this can result in issues\n");
+			DRM_INFO("when using vblank-synced partial screen updates.\n");
+			dev_priv->gt.force_wake_get = __gen6_gt_force_wake_get;
+			dev_priv->gt.force_wake_put = __gen6_gt_force_wake_put;
+		}
 	} else if (IS_GEN6(dev)) {
 		dev_priv->gt.force_wake_get = __gen6_gt_force_wake_get;
 		dev_priv->gt.force_wake_put = __gen6_gt_force_wake_put;
--
1.8.1.2