linux-kernel - Re: [PATCH] ACPI: make acpi

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Date:	Wed, 21 Jul 2010 17:53:25 -0700
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	Len Brown <lenb@...nel.org>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	"Yu, Luming" <luming.yu@...el.com>,
	Philip Langdale <philipl@...rt.org>,
	Jeff Garrett <jeff@...rrett.org>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH] ACPI: make acpi_idle Nehalem-aware

On Wed, Jul 21, 2010 at 2:31 PM, Len Brown <lenb@...nel.org> wrote:
> From: Len Brown <len.brown@...el.com>
>
> 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@...el.com>
> ---
>  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
>
>
>
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