From 859deea949c382d9ccb6397fe33df3703ecef45d Mon Sep 17 00:00:00 2001 From: Benjamin Herrenschmidt Date: Fri, 20 Oct 2006 14:37:05 +1000 Subject: [POWERPC] Cell timebase bug workaround The Cell CPU timebase has an erratum. When reading the entire 64 bits of the timebase with one mftb instruction, there is a handful of cycles window during which one might read a value with the low order 32 bits already reset to 0x00000000 but the high order bits not yet incremeted by one. This fixes it by reading the timebase again until the low order 32 bits is no longer 0. That might introduce occasional latencies if hitting mftb just at the wrong time, but no more than 70ns on a cell blade, and that was considered acceptable. Signed-off-by: Benjamin Herrenschmidt Acked-by: Olof Johansson Signed-off-by: Paul Mackerras --- arch/powerpc/kernel/vdso64/gettimeofday.S | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'arch') diff --git a/arch/powerpc/kernel/vdso64/gettimeofday.S b/arch/powerpc/kernel/vdso64/gettimeofday.S index 56e76ff5498f..40ffd9b6cef7 100644 --- a/arch/powerpc/kernel/vdso64/gettimeofday.S +++ b/arch/powerpc/kernel/vdso64/gettimeofday.S @@ -229,8 +229,10 @@ V_FUNCTION_BEGIN(__do_get_xsec) xor r0,r8,r8 /* create dependency */ add r3,r3,r0 - /* Get TB & offset it */ - mftb r7 + /* Get TB & offset it. We use the MFTB macro which will generate + * workaround code for Cell. + */ + MFTB(r7) ld r9,CFG_TB_ORIG_STAMP(r3) subf r7,r9,r7 -- cgit v1.2.3