From a21d3396b8150b3a776534520fc8ec29809ab4b8 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Mon, 14 Nov 2011 17:24:58 +0100 Subject: [PATCH] ARM: 7161/1: errata: no automatic store buffer drain 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 Tested-by: Marc Zyngier Signed-off-by: Will Deacon Signed-off-by: Russell King Signed-off-by: Paul Gortmaker --- 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 811dedc6c68db..3ee6a06c7503b 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 acf5e6fdb6dcb..7f170f4238d20 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(); -- 2.47.3