From 30a564be9d9554c168a654eddc2165869cc0d7bf Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 13 Apr 2010 15:31:36 +0200 Subject: x86, hpet: Restrict read back to affected ATI chipsets After programming the HPET, we do a readback as a workaround for ATI/SBx00 chipsets as a synchronization. Unfortunately this triggers an erratum in newer ICH chipsets (ICH9+) where reading the comparator immediately after the write returns the old value. Furthermore, as always, I/O reads are bad for performance. Therefore, restrict the readback to the chipsets that need it, or, for debugging purposes, when we are running with hpet=verbose. Signed-off-by: Thomas Gleixner Acked-by: Venkatesh Pallipadi LKML-Reference: <20100225185348.GA9674@linux-os.sc.intel.com> Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/hpet.h | 1 + 1 file changed, 1 insertion(+) (limited to 'arch/x86/include') diff --git a/arch/x86/include/asm/hpet.h b/arch/x86/include/asm/hpet.h index 1d5c08a1bdf..004e6e25e91 100644 --- a/arch/x86/include/asm/hpet.h +++ b/arch/x86/include/asm/hpet.h @@ -68,6 +68,7 @@ extern unsigned long force_hpet_address; extern u8 hpet_blockid; extern int hpet_force_user; extern u8 hpet_msi_disable; +extern u8 hpet_readback_cmp; extern int is_hpet_enabled(void); extern int hpet_enable(void); extern void hpet_disable(void); -- cgit v1.2.3-18-g5258