From 931db7d6880027bb2b6b0cb78a488ab1486e28b7 Mon Sep 17 00:00:00 2001 From: Lennert Buytenhek Date: Sat, 29 Oct 2005 16:28:26 +0100 Subject: [ARM] 3050/1: remove ixp2000_reg_write erratum #66 workaround Patch from Lennert Buytenhek The workaround that we do for avoiding triggering ixp2400 erratum #66 involves mapping I/O pages using XCB=101 instead of XCB=000 so that we prevent the I/O signal to the gasket from being asserted (which can cause data corruption.) But XCB=101 mappings are write-buffered while mappings using XCB=000 are not, which is why if we use XCB=101 mappings we do a readback for every CSR store in an attempt to make sure that the store has been pushed out of the xscale core and the gasket. Unfortunately, there are two issues with this: - we do a readback for every CSR store, which is wrong, because the register we are writing to might have unwanted side-effects on read, for example, in the case of the scratchpad ring enqueue/dequeue registers; and - the readback is totally ineffective in the way we currently do it, because we just issue a load but do not issue any instruction that depends on the return value of that load, so the xscale core does not wait for the load to complete before continuing. See this linux-arm-kernel mailing list post for further information: http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2005-September/031314.html This means that my ixp2400 boxes have been running for many months without a working readback in ixp2000_reg_write, without any apparent adverse effects. Two of them have been running for a week now with the actual readback deleted from ixp2000_reg_write, also without any apparent ill effects. So, because in its current form it does more harm than good, the readback in ixp2000_reg_write should simply be killed, as the patch below does. Signed-off-by: Lennert Buytenhek Signed-off-by: Deepak Saxena Signed-off-by: Russell King --- include/asm-arm/arch-ixp2000/platform.h | 29 ----------------------------- 1 file changed, 29 deletions(-) (limited to 'include/asm-arm/arch-ixp2000/platform.h') diff --git a/include/asm-arm/arch-ixp2000/platform.h b/include/asm-arm/arch-ixp2000/platform.h index abdcf51bd28..aabeef2454d 100644 --- a/include/asm-arm/arch-ixp2000/platform.h +++ b/include/asm-arm/arch-ixp2000/platform.h @@ -15,39 +15,10 @@ #ifndef __ASSEMBLY__ -/* - * The IXP2400 B0 silicon contains an erratum (#66) that causes writes - * to on-chip I/O register to not complete fully. What this means is - * that if you have a write to on-chip I/O followed by a back-to-back - * read or write, the first write will happen twice. OR...if it's - * not a back-to-back transaction, the read or write will generate - * incorrect data. - * - * The official work around for this is to set the on-chip I/O regions - * as XCB=101 and then force a read-back from the register. - * - */ -#if defined(CONFIG_ARCH_ENP2611) || defined(CONFIG_ARCH_IXDP2400) || defined(CONFIG_ARCH_IXDP2401) - -#include /* Pickup local_irq_ functions */ - -static inline void ixp2000_reg_write(volatile void *reg, unsigned long val) -{ - unsigned long dummy; - unsigned long flags; - - local_irq_save(flags); - *((volatile unsigned long *)reg) = val; - barrier(); - dummy = *((volatile unsigned long *)reg); - local_irq_restore(flags); -} -#else static inline void ixp2000_reg_write(volatile void *reg, unsigned long val) { *((volatile unsigned long *)reg) = val; } -#endif /* IXDP2400 || IXDP2401 */ #define ixp2000_reg_read(reg) (*((volatile unsigned long *)reg)) /* -- cgit v1.2.3-70-g09d2 From ecbea7a2dae94092db9566bcd1f38535e9b3cde9 Mon Sep 17 00:00:00 2001 From: Lennert Buytenhek Date: Sat, 29 Oct 2005 16:28:27 +0100 Subject: [ARM] 3051/1: turn ixp2000_reg_read into an inline function Patch from Lennert Buytenhek Turn ixp2000_reg_read into an inline function. Signed-off-by: Lennert Buytenhek Signed-off-by: Deepak Saxena Signed-off-by: Russell King --- include/asm-arm/arch-ixp2000/platform.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'include/asm-arm/arch-ixp2000/platform.h') diff --git a/include/asm-arm/arch-ixp2000/platform.h b/include/asm-arm/arch-ixp2000/platform.h index aabeef2454d..6e5b6a955ab 100644 --- a/include/asm-arm/arch-ixp2000/platform.h +++ b/include/asm-arm/arch-ixp2000/platform.h @@ -15,11 +15,15 @@ #ifndef __ASSEMBLY__ +static inline unsigned long ixp2000_reg_read(volatile void *reg) +{ + return *((volatile unsigned long *)reg); +} + static inline void ixp2000_reg_write(volatile void *reg, unsigned long val) { *((volatile unsigned long *)reg) = val; } -#define ixp2000_reg_read(reg) (*((volatile unsigned long *)reg)) /* * Boards may multiplex different devices on the 2nd channel of -- cgit v1.2.3-70-g09d2 From b4a1f67fbfb848ded8cf0c6c305224534144ab2d Mon Sep 17 00:00:00 2001 From: Lennert Buytenhek Date: Sat, 29 Oct 2005 16:28:28 +0100 Subject: [ARM] 3053/1: introduce ixp2000_reg_wrb (ixp2000_reg_write plus readback) Patch from Lennert Buytenhek Introduce ixp2000_reg_wrb, which is a variant of ixp2000_reg_write that does a readback from the target register, to make sure that the write has been flushed out of the write buffer. Unlike the previous (ineffective) readback in ixp2000_reg_write, this readback is followed by an instruction that depends on the value of the readback so that the CPU actually stalls until the readback has completed. Signed-off-by: Lennert Buytenhek Signed-off-by: Deepak Saxena Signed-off-by: Russell King --- include/asm-arm/arch-ixp2000/platform.h | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) (limited to 'include/asm-arm/arch-ixp2000/platform.h') diff --git a/include/asm-arm/arch-ixp2000/platform.h b/include/asm-arm/arch-ixp2000/platform.h index 6e5b6a955ab..a66317ab207 100644 --- a/include/asm-arm/arch-ixp2000/platform.h +++ b/include/asm-arm/arch-ixp2000/platform.h @@ -25,6 +25,31 @@ static inline void ixp2000_reg_write(volatile void *reg, unsigned long val) *((volatile unsigned long *)reg) = val; } +/* + * On the IXP2400, we can't use XCB=000 due to chip bugs. We use + * XCB=101 instead, but that makes all I/O accesses bufferable. This + * is not a problem in general, but we do have to be slightly more + * careful because I/O writes are no longer automatically flushed out + * of the write buffer. + * + * In cases where we want to make sure that a write has been flushed + * out of the write buffer before we proceed, for example when masking + * a device interrupt before re-enabling IRQs in CPSR, we can use this + * function, ixp2000_reg_wrb, which performs a write, a readback, and + * issues a dummy instruction dependent on the value of the readback + * (mov rX, rX) to make sure that the readback has completed before we + * continue. + */ +static inline void ixp2000_reg_wrb(volatile void *reg, unsigned long val) +{ + unsigned long dummy; + + *((volatile unsigned long *)reg) = val; + + dummy = *((volatile unsigned long *)reg); + __asm__ __volatile__("mov %0, %0" : "+r" (dummy)); +} + /* * Boards may multiplex different devices on the 2nd channel of * the slowport interface that each need different configuration -- cgit v1.2.3-70-g09d2