[ 3.8.y.z extended stable ] Patch "drm/i915: Serialize almost all register access" has been added to staging queue

[Kamal Mostafa]

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

    drm/i915: Serialize almost all register access

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 4dda4ec438e3e43de4db14195fa7f413394d17d8 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris at chris-wilson.co.uk>
Date: Fri, 19 Jul 2013 20:36:51 +0100
Subject: drm/i915: Serialize almost all register access

commit a7cd1b8fea2f341b626b255d9898a5ca5fabbf0a upstream.

In theory, the different register blocks were meant to be only ever
touched when holding either the struct_mutex, mode_config.lock or even a
specific localised lock. This does not seem to be the case, and the
hardware reacts extremely badly if we attempt to concurrently access two
registers within the same cacheline.

The HSD suggests that we only need to do this workaround for display
range registers. However, upon review we need to serialize the multiple
stages in our register write functions - if only for preemption
protection.

Irrespective of the hardware requirements, the current io functions are
a little too loose with respect to the combination of pre- and
post-condition testing that we do in conjunction with the actual io. As
a result, we may be pre-empted and generate both false-postive and
false-negative errors.

Note well that this is a "90%" solution, there remains a few direct
users of ioread/iowrite which will be fixed up in the next few patches.
Since they are more invasive and that this simple change will prevent
almost all lockups on Haswell, we kept this patch simple to facilitate
backporting to stable.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=63914
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
[ kamal: backport to 3.8 ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/i915/i915_drv.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 41e02dc..5e50875 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -1247,23 +1247,23 @@ ilk_dummy_write(struct drm_i915_private *dev_priv)

 #define __i915_read(x, y) \
 u##x i915_read##x(struct drm_i915_private *dev_priv, u32 reg) { \
+	unsigned long irqflags; \
 	u##x val = 0; \
+	spin_lock_irqsave(&dev_priv->gt_lock, irqflags); \
 	if (IS_GEN5(dev_priv->dev)) \
 		ilk_dummy_write(dev_priv); \
 	if (NEEDS_FORCE_WAKE((dev_priv), (reg))) { \
-		unsigned long irqflags; \
-		spin_lock_irqsave(&dev_priv->gt_lock, irqflags); \
 		if (dev_priv->forcewake_count == 0) \
 			dev_priv->gt.force_wake_get(dev_priv); \
 		val = read##y(dev_priv->regs + reg); \
 		if (dev_priv->forcewake_count == 0) \
 			dev_priv->gt.force_wake_put(dev_priv); \
-		spin_unlock_irqrestore(&dev_priv->gt_lock, irqflags); \
 	} else if (IS_VALLEYVIEW(dev_priv->dev) && IS_DISPLAYREG(reg)) { \
 		val = read##y(dev_priv->regs + reg + 0x180000);		\
 	} else { \
 		val = read##y(dev_priv->regs + reg); \
 	} \
+	spin_unlock_irqrestore(&dev_priv->gt_lock, irqflags); \
 	trace_i915_reg_rw(false, reg, val, sizeof(val)); \
 	return val; \
 }
@@ -1276,8 +1276,10 @@ __i915_read(64, q)

 #define __i915_write(x, y) \
 void i915_write##x(struct drm_i915_private *dev_priv, u32 reg, u##x val) { \
+	unsigned long irqflags; \
 	u32 __fifo_ret = 0; \
 	trace_i915_reg_rw(true, reg, val, sizeof(val)); \
+	spin_lock_irqsave(&dev_priv->gt_lock, irqflags); \
 	if (NEEDS_FORCE_WAKE((dev_priv), (reg))) { \
 		__fifo_ret = __gen6_gt_wait_for_fifo(dev_priv); \
 	} \
@@ -1299,6 +1301,7 @@ void i915_write##x(struct drm_i915_private *dev_priv, u32 reg, u##x val) { \
 		DRM_ERROR("Unclaimed write to %x\n", reg); \
 		writel(ERR_INT_MMIO_UNCLAIMED, dev_priv->regs + GEN7_ERR_INT);	\
 	} \
+	spin_unlock_irqrestore(&dev_priv->gt_lock, irqflags); \
 }
 __i915_write(8, b)
 __i915_write(16, w)
--
1.8.1.2