Messages in this thread | | | Date | Wed, 7 Aug 2019 12:41:18 +0100 | From | Sudeep Holla <> | Subject | Re: [PATCH] ACPI / CPPC: do not require the _PSD method when using CPPC |
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On Mon, Aug 05, 2019 at 11:03:38AM -0600, Al Stone wrote: > According to the ACPI 6.3 specification, the _PSD method is optional > when using CPPC. The underlying assumption appears to be that each CPU > can change frequency independently from all other CPUs; _PSD is provided > to tell the OS that some processors can NOT do that. > > However, the acpi_get_psd() function returns -ENODEV if there is no _PSD > method present, or an ACPI error status if an error occurs when evaluating > _PSD, if present. This essentially makes _PSD mandatory when using CPPC, > in violation of the specification, and only on Linux. > > This has forced some firmware writers to provide a dummy _PSD, even though > it is irrelevant, but only because Linux requires it; other OSPMs follow > the spec. We really do not want to have OS specific ACPI tables, though. > > So, correct acpi_get_psd() so that it does not return an error if there > is no _PSD method present, but does return a failure when the method can > not be executed properly. This allows _PSD to be optional as it should > be. >
Makes sense to me. FWIW,
Reviewed-by: Sudeep Holla < sudeep.holla@arm.com>
-- Regards, Sudeep
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