Patch "drm/i915: Replace WARN inside I915_READ64_2x32 with retry loop" has been added to the 4.1-stable tree

Patch "drm/i915: Replace WARN inside I915_READ64_2x32 with retry loop" has been added to the 4.1-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    drm/i915: Replace WARN inside I915_READ64_2x32 with retry loop

to the 4.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-i915-replace-warn-inside-i915_read64_2x32-with-retry-loop.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From ee0a227b7ac6e75f28e10269f81c7ec6eb600952 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Wed, 15 Jul 2015 09:50:42 +0100
Subject: drm/i915: Replace WARN inside I915_READ64_2x32 with retry loop
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Chris Wilson <chris@chris-wilson.co.uk>

commit ee0a227b7ac6e75f28e10269f81c7ec6eb600952 upstream.

Since we may conceivably encounter situations where the upper part of the
64bit register changes between reads, for example when a timestamp
counter overflows, change the WARN into a retry loop.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/i915/i915_drv.h |   17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3190,15 +3190,14 @@ int intel_freq_opcode(struct drm_i915_pr
 #define I915_READ64(reg)	dev_priv->uncore.funcs.mmio_readq(dev_priv, (reg), true)
 
 #define I915_READ64_2x32(lower_reg, upper_reg) ({			\
-		u32 upper = I915_READ(upper_reg);			\
-		u32 lower = I915_READ(lower_reg);			\
-		u32 tmp = I915_READ(upper_reg);				\
-		if (upper != tmp) {					\
-			upper = tmp;					\
-			lower = I915_READ(lower_reg);			\
-			WARN_ON(I915_READ(upper_reg) != upper);		\
-		}							\
-		(u64)upper << 32 | lower; })
+	u32 upper, lower, tmp;						\
+	tmp = I915_READ(upper_reg);					\
+	do {								\
+		upper = tmp;						\
+		lower = I915_READ(lower_reg);				\
+		tmp = I915_READ(upper_reg);				\
+	} while (upper != tmp);						\
+	(u64)upper << 32 | lower; })
 
 #define POSTING_READ(reg)	(void)I915_READ_NOTRACE(reg)
 #define POSTING_READ16(reg)	(void)I915_READ16_NOTRACE(reg)


Patches currently in stable-queue which might be from chris@chris-wilson.co.uk are

queue-4.1/drm-i915-declare-the-swizzling-unknown-for-l-shaped-configurations.patch
queue-4.1/drm-i915-replace-warn-inside-i915_read64_2x32-with-retry-loop.patch