On Sat, 2016-03-26 at 01:56 +0100, Rafael J. Wysocki wrote: > On Thu, Mar 24, 2016 at 5:07 AM, Srinivas Pandruvada > <srinivas.pandruvada@xxxxxxxxxxxxxxx> 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@linux.intel > > .com> > > I've queued it up, but I have modified the subject and the changelog > and renamed the new function. > > Please have a look at > http://git.kernel.org/cgit/linux/kernel/git/rafael/linux-pm.git/commi > t/?h=bleeding-edge&id=42341f87ba1bee4c5be95038c24abb69cbcf361a > and let me know if it makes sense to you. Looks fine to me. Thanks, Srinivas > > Thanks, > Rafael -- 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
