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Commit 11ed0ba1 authored by Will Deacon's avatar Will Deacon Committed by Russell King
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ARM: 7161/1: errata: no automatic store buffer drain 



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.

Cc: stable@vger.kernel.org
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Tested-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 6fe4c6d4

arch/arm/Kconfig

+12 −0
Original line number Diff line number Diff line
@@ -1352,6 +1352,18 @@ config ARM_ERRATA_764369 
	  relevant cache maintenance functions and sets a specific bit

	  in the diagnostic control register of the SCU.



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



source "arch/arm/common/Kconfig"

arch/arm/kernel/process.c

+3 −0
Original line number Diff line number Diff line
@@ -192,6 +192,9 @@ void cpu_idle(void) 
#endif



			local_irq_disable();

#ifdef CONFIG_PL310_ERRATA_769419

			wmb();

#endif

			if (hlt_counter) {

				local_irq_enable();

				cpu_relax();