On Wed, Jul 21, 2010 at 2:31 PM, Len Brown <lenb@xxxxxxxxxx> wrote: > From: Len Brown <len.brown@xxxxxxxxx> > > The BIOS exports deep C-states on modern Intel processors > as "C3-type" to satisfy various legacy Operating Systems. > > However, the hardware actually supports C2-type, and does > not require the extra costs of C3-type. > > One of the costs is to check the BM_STS (Bus Master Status) > bit before entering C3, and instead choose a shallower C-state > if there was "recent bus master activity". > > We have found a number of systems in the field that erroneously > set BM_STS and prevent entry into deep C-states. > Re-define BIOS presented C3-type states as C2-type states > on modern processors to avoid this issue. > > If a device in the system really does want to prevent use > of a deep C-state, its Linux driver should register its > constraints via pm_qos_add_request(). > > https://bugzilla.kernel.org/show_bug.cgi?id=15886 > Agree with the intent. But, I think its cleaner to keep all arch model checks in arch/x86/kernel/acpi/cstate.c. Thanks, Venki > Signed-off-by: Len Brown <len.brown@xxxxxxxxx> > --- > drivers/acpi/processor_idle.c | 38 ++++++++++++++++++++++++++++++++++++++ > 1 files changed, 38 insertions(+), 0 deletions(-) > > diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c > index b1b3856..14d1a0c 100644 > --- a/drivers/acpi/processor_idle.c > +++ b/drivers/acpi/processor_idle.c > @@ -607,6 +607,38 @@ static void acpi_processor_power_verify_c3(struct acpi_processor *pr, > return; > } > > +/* > + * Modern Intel processors support only ACPI C2-type C-states. > + * But the BIOS tends to report its deepest C-state as C3-type > + * to satisfy various old operating systems. We can skip > + * C3 OS overhead by treating the deep-states as C2-type. > + * Also, we can avoid checking BM_STS, which on some systems > + * erroneously prevents entry into C3-type states. > + */ > +static int acpi_c3type_is_really_c2type(void) { > + > + if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) > + return 0; > + > + if (boot_cpu_data.x86 != 6) > + return 0; > + > + switch(boot_cpu_data.x86_model) { > + case 0x1A: /* Core i7, Xeon 5500 series */ > + case 0x1E: /* Core i7 and i5 Processor */ > + case 0x1F: /* Core i7 and i5 Processor */ > + case 0x2E: /* NHM-EX Xeon */ > + case 0x2F: /* WSM-EX Xeon */ > + case 0x25: /* WSM */ > + case 0x2C: /* WSM */ > + case 0x2A: /* SNB */ > + case 0x2D: /* SNB Xeon */ > + return 1; > + default: > + return 0; > + } > +} > + > static int acpi_processor_power_verify(struct acpi_processor *pr) > { > unsigned int i; > @@ -617,6 +649,12 @@ static int acpi_processor_power_verify(struct acpi_processor *pr) > for (i = 1; i < ACPI_PROCESSOR_MAX_POWER && i <= max_cstate; i++) { > struct acpi_processor_cx *cx = &pr->power.states[i]; > > + if ((cx->type == ACPI_STATE_C3) > + && acpi_c3type_is_really_c2type()) { > + ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Redefining C3-type to C2\n")); > + cx->type = ACPI_STATE_C2; > + } > + > switch (cx->type) { > case ACPI_STATE_C1: > cx->valid = 1; > -- > 1.7.2.rc3.43.g24e7a > > > -- 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
