On Thu, 5 Jun 2008, Zhao Yakui wrote: > Subject: ACPI: Disable the C2C3_FFH access mode if MWAIT is unsupported > From: Zhao Yakui <yakui.zhao@xxxxxxxxx> > > After the following commit is merged, C2C3_FFH mode will be enabled and > passed into the _PDC object. But because MWAIT is unsupported on some laptops, > the different power states will be returned by the _CST object. > Maybe it will be better to disable C2C3_FFH access mode if MWAIT is unsupported. > > commit 991528d7348667924176f3e29addea0675298944 > Author: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx> > Date: Mon Sep 25 16:28:13 2006 -0700 > > ACPI: Processor native C-states using MWAIT > http://bugzilla.kernel.org/show_bug.cgi?id=10807 Interesting bug report. Unfortunately, it is a BIOS bug that the BIOS exposes C3 when the OS doesn't support MWAIT, but neglects to expose C3 when the OS does support MWAIT. This patch will have no effect on the system in the bug report. Indeed, it would benefit only a system with a BIOS that thinks it has MWAIT support but a CPU that thinks it doesn't... probably good hygine to do this, but I don't think it will help anything. I think the fix for the machine in bug 10807 is to have a bootparam that disables mwait support, say "idle=!mwait" and a DMI entry for that box that invokes it to work around the BIOS bug. thanks, -Len > Signed-off-by: Zhao Yakui <yakui.zhao@xxxxxxxxx> > Signed-off-by: Li Shaohua <shaohua.li@xxxxxxxxx> > > --- > arch/x86/kernel/acpi/processor.c | 5 +++++ > 1 file changed, 5 insertions(+) > > Index: linux-2.6/arch/x86/kernel/acpi/processor.c > =================================================================== > --- linux-2.6.orig/arch/x86/kernel/acpi/processor.c > +++ linux-2.6/arch/x86/kernel/acpi/processor.c > @@ -43,6 +43,11 @@ static void init_intel_pdc(struct acpi_p > buf[0] = ACPI_PDC_REVISION_ID; > buf[1] = 1; > buf[2] = ACPI_PDC_C_CAPABILITY_SMP; > + /* > + * If mwait/monitor is unsupported, C2/C3_FFH will be disabled. > + */ > + if (!cpu_has(c, X86_FEATURE_MWAIT)) > + buf[2] &= ~ACPI_PDC_C_C2C3_FFH; > > /* > * The default of PDC_SMP_T_SWCOORD bit is set for intel x86 cpu so > > -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
