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authorThomas Gleixner <tglx@linutronix.de>2010-04-13 15:31:36 +0200
committerH. Peter Anvin <hpa@zytor.com>2010-04-28 18:14:29 -0700
commit30a564be9d9554c168a654eddc2165869cc0d7bf (patch)
tree734de780e0f84a189f66ca3cbf611e6f2bc563e9 /arch/x86/include/asm/hpet.h
parent1d16b0f2f3edf05f12a9e3960588e0d4854157bb (diff)
downloadlinux-30a564be9d9554c168a654eddc2165869cc0d7bf.tar.bz2
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 <tglx@linutronix.de> Acked-by: Venkatesh Pallipadi <venki@google.com> LKML-Reference: <20100225185348.GA9674@linux-os.sc.intel.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/include/asm/hpet.h')
-rw-r--r--arch/x86/include/asm/hpet.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/x86/include/asm/hpet.h b/arch/x86/include/asm/hpet.h
index 1d5c08a1bdfd..004e6e25e913 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);