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Date: Wed, 23 Mar 2016 12:43:33 -0400
From: Linda Knippers <linda.knippers@....com>
To: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
rjw@...ysocki.net
Cc: tony.luck@...el.com, bp@...en8.de, tglx@...utronix.de,
mingo@...hat.com, hpa@...or.com, lenb@...nel.org,
linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-acpi@...r.kernel.org
Subject: Re: [PATCH v6] acpi: Issue _OSC call for native thermal interrupt
handling
I raised a general concern on a previous patch so I found a 1P server
with Skylake and HWP to try. This doesn't qualify as a tested-by
since all I did was apply the patch and boot the server but hey, it booted.
I do have a question below...
On 3/23/2016 12:07 AM, Srinivas Pandruvada wrote:
> There are several reports of freeze on enabling HWP (Hardware PStates)
> feature on Skylake based systems by Intel P states driver. The root
> cause is identified as the HWP interrupts causing BIOS code to freeze.
> HWP interrupts uses thermal LVT.
> Linux natively handles thermal interrupts, but in Skylake based systems
> SMM will take control of thermal interrupts. This is a problem for several
> reasons:
> - It is freezing in BIOS when tries to handle thermal interrupt, which
> will require BIOS upgrade
> - With SMM handling thermal we loose all the reporting features of
> Linux arch/x86/kernel/cpu/mcheck/therm_throt driver
> - Some thermal drivers like x86-package-temp driver depends on the thermal
> threshold interrupts
> - The HWP interrupts are useful for debugging and tuning performance
>
> So we need native handling of thermal interrupts. This requires some
> way to inform SMM that OS can handle thermal interrupts. This can be
> done by using _OSC/_PDC under processor scope very early in ACPI
> initialization flow.
> The bit 12 of _OSC/_PDC in processor scope defines whether OS supports
> handling of native interrupts for Collaborative Processor Performance
> Control (CPPC) notifications. Since HWP is a implementation of CPPC,
> setting this bit is equivalent to inform SMM that OS is capable of
> handling thermal interrupts.
> Refer to this document for details on _OSC/_PDC
> http://www.intel.com/content/www/us/en/standards/processor-vendor-
> specific-acpi-specification.html
>
> This change introduces a new function acpi_early_processor_set_osc(),
> which walks acpi name space and finds acpi processor object and
> set capability via _OSC method.
>
> Also this change writes HWP status bits to 0 to clear any HWP status
> bits in intel_thermal_interrupt().
>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> ---
> v6:
> Added __init for two functions and moved dummy function to internal.h
> Shortened the name of the function.
>
> v5:
> No code change. Changed commit message to explain HWP is a implementation
> of CPPC.
>
> v4:
> Suggestion by Boris for removing use of intermediate variable for
> clearing HWP status and using boot_cpu_has instead of static_cpu_has
>
> v3:
> - Added CONFIG_X86 around static_cpu_has() to fix compile error on
> ARCH=ia64, reported by kbuild test robot
> - return AE_CTRL_TERMINATE to terminate acpi name walk space, when _OSC
> is set already once.
> v2:
> Unnecessary newline was introduced, removed that in acpi_processor.c
>
> arch/x86/kernel/cpu/mcheck/therm_throt.c | 3 +++
> drivers/acpi/acpi_processor.c | 44 ++++++++++++++++++++++++++++++++
> drivers/acpi/bus.c | 3 +++
> drivers/acpi/internal.h | 6 +++++
> 4 files changed, 56 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/mcheck/therm_throt.c b/arch/x86/kernel/cpu/mcheck/therm_throt.c
> index 2c5aaf8..0553858 100644
> --- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
> +++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
> @@ -385,6 +385,9 @@ static void intel_thermal_interrupt(void)
> {
> __u64 msr_val;
>
> + if (static_cpu_has(X86_FEATURE_HWP))
> + wrmsrl_safe(MSR_HWP_STATUS, 0);
> +
> rdmsrl(MSR_IA32_THERM_STATUS, msr_val);
>
> /* Check for violation of core thermal thresholds*/
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index 6979186..ba50f46 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -491,6 +491,50 @@ static void acpi_processor_remove(struct acpi_device *device)
> }
> #endif /* CONFIG_ACPI_HOTPLUG_CPU */
>
> +#ifdef CONFIG_X86
> +static bool acpi_hwp_native_thermal_lvt_set;
> +static acpi_status __init acpi_hwp_native_thermal_lvt_osc(acpi_handle handle,
> + u32 lvl,
> + void *context,
> + void **rv)
> +{
> + u8 sb_uuid_str[] = "4077A616-290C-47BE-9EBD-D87058713953";
> + u32 capbuf[2];
> + struct acpi_osc_context osc_context = {
> + .uuid_str = sb_uuid_str,
> + .rev = 1,
> + .cap.length = 8,
> + .cap.pointer = capbuf,
> + };
> +
> + if (acpi_hwp_native_thermal_lvt_set)
> + return AE_CTRL_TERMINATE;
> +
> + capbuf[0] = 0x0000;
> + capbuf[1] = 0x1000; /* set bit 12 */
> +
> + if (ACPI_SUCCESS(acpi_run_osc(handle, &osc_context))) {
> + acpi_hwp_native_thermal_lvt_set = true;
> + kfree(osc_context.ret.pointer);
There are other boot messages that indicate when something is happening
with _OSC. Should there be one for this? Or is there some other obvious
way one can know that this was set?
> + }
> +
> + return AE_OK;
> +}
> +
> +void __init acpi_early_processor_set_osc(void)
> +{
> + if (boot_cpu_has(X86_FEATURE_HWP)) {
> + acpi_walk_namespace(ACPI_TYPE_PROCESSOR, ACPI_ROOT_OBJECT,
> + ACPI_UINT32_MAX,
> + acpi_hwp_native_thermal_lvt_osc,
> + NULL, NULL, NULL);
> + acpi_get_devices(ACPI_PROCESSOR_DEVICE_HID,
> + acpi_hwp_native_thermal_lvt_osc,
> + NULL, NULL);
> + }
> +}
> +#endif
> +
> /*
> * The following ACPI IDs are known to be suitable for representing as
> * processor devices.
> diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> index 891c42d..7e73aea 100644
> --- a/drivers/acpi/bus.c
> +++ b/drivers/acpi/bus.c
> @@ -1005,6 +1005,9 @@ static int __init acpi_bus_init(void)
> goto error1;
> }
>
> + /* Set capability bits for _OSC under processor scope */
> + acpi_early_processor_set_osc();
> +
> /*
> * _OSC method may exist in module level code,
> * so it must be run after ACPI_FULL_INITIALIZATION
> diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
> index 1e6833a..9f34051b 100644
> --- a/drivers/acpi/internal.h
> +++ b/drivers/acpi/internal.h
> @@ -138,6 +138,12 @@ void acpi_early_processor_set_pdc(void);
> static inline void acpi_early_processor_set_pdc(void) {}
> #endif
>
> +#ifdef CONFIG_X86
> +void acpi_early_processor_set_osc(void);
> +#else
> +static inline void acpi_early_processor_set_osc(void) {}
> +#endif
> +
> /* --------------------------------------------------------------------------
> Embedded Controller
> -------------------------------------------------------------------------- */
>
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