x86, hpet: Restrict read back to affected ATI chipsets

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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>

...

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Thomas Gleixner 2010-04-13 15:31:36 +02:00 • committed by H. Peter Anvin

parent 1d16b0f2f3

commit 30a564be9d

3 changed files with 23 additions and 12 deletions

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1

arch/x86/include/asm/hpet.h

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29

arch/x86/kernel/hpet.c

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5

arch/x86/kernel/quirks.c

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