linux-kernel - [v2.6.34-stable 23/77] ARM: 7161/1: errata: no automatic store buffer drain

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Date:	Tue, 8 Jan 2013 18:35:02 -0500
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	<stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:	Will Deacon <will.deacon@....com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [v2.6.34-stable 23/77] ARM: 7161/1: errata: no automatic store buffer drain

From: Will Deacon <will.deacon@....com>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 11ed0ba1754841316d4095478944300acf19acc3 upstream.

This patch implements a workaround for PL310 erratum 769419. On
revisions of the PL310 prior to r3p2, the Store Buffer does not
automatically drain. This can cause normal, non-cacheable writes to be
retained when the memory system is idle, leading to suboptimal I/O
performance for drivers using coherent DMA.

This patch adds an optional wmb() call to the cpu_idle loop. On systems
with an outer cache, this causes an explicit flush of the store buffer.

Acked-by: Catalin Marinas <catalin.marinas@....com>
Tested-by: Marc Zyngier <marc.zyngier@....com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 arch/arm/Kconfig          | 12 ++++++++++++
 arch/arm/kernel/process.c |  3 +++
 2 files changed, 15 insertions(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 811dedc..3ee6a06 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1380,6 +1380,18 @@ config UACCESS_WITH_MEMCPY
 	  However, if the CPU data cache is using a write-allocate mode,
 	  this option is unlikely to provide any performance gain.
 
+config PL310_ERRATA_769419
+	bool "PL310 errata: no automatic Store Buffer drain"
+	depends on CACHE_L2X0
+	help
+	  On revisions of the PL310 prior to r3p2, the Store Buffer does
+	  not automatically drain. This can cause normal, non-cacheable
+	  writes to be retained when the memory system is idle, leading
+	  to suboptimal I/O performance for drivers using coherent DMA.
+	  This option adds a write barrier to the cpu_idle loop so that,
+	  on systems with an outer cache, the store buffer is drained
+	  explicitly.
+
 endmenu
 
 menu "Boot options"
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index acf5e6f..7f170f4 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -155,6 +155,9 @@ void cpu_idle(void)
 #endif
 
 			local_irq_disable();
+#ifdef CONFIG_PL310_ERRATA_769419
+			wmb();
+#endif
 			if (hlt_counter) {
 				local_irq_enable();
 				cpu_relax();
-- 
1.7.12.1

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