Re: [PATCH v2.1 1/8] ACPI: bus: Fix handling of _OSC errors in acpi_run_osc()

[Jonathan Cameron <jonathan.cameron@huawei.com>]

On Mon, 22 Dec 2025 20:05:44 +0100
"Rafael J. Wysocki" <rafael@kernel.org> wrote:

> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> The handling of _OSC errors in acpi_run_osc() is inconsistent and
> arguably not compliant with the _OSC definition (cf. Section 6.2.12 of
> ACPI 6.6 [1]).
> 
> Namely, if OSC_QUERY_ENABLE is not set in the capabilities buffer and
> any of the error bits are set in the _OSC return buffer, acpi_run_osc()
> returns an error code and the _OSC return buffer is discarded.  However,
> in that case, depending on what error bits are set, the return buffer
> may contain acknowledged bits for features that need to be controlled by
> the kernel going forward.
> 
> If the OSC_INVALID_UUID_ERROR bit is set, the request could not be
> processed at all and so in that particular case discarding the _OSC
> return buffer and returning an error is the right thing to do regardless
> of whether or not OSC_QUERY_ENABLE is set in the capabilities buffer.
> 
> If OSC_QUERY_ENABLE is set in the capabilities buffer and the
> OSC_REQUEST_ERROR or OSC_INVALID_REVISION_ERROR bits are set in the
> return buffer, acpi_run_osc() may return an error and discard the _OSC
> return buffer because in that case the platform configuration does not
> change.  However, if any of them is set in the return buffer when
> OSC_QUERY_ENABLE is not set in the capabilities buffer, the feature
> mask in the _OSC return buffer still representes a set of acknowleded

typo: represents

> features as per the _OSC definition:
> 
>  The platform acknowledges the Capabilities Buffer by returning a
>  buffer of DWORDs of the same length. Set bits indicate acknowledgment
>  that OSPM may take control of the capability and cleared bits indicate
>  that the platform either does not support the capability or that OSPM
>  may not assume control.
> 
> which is not conditional on the error bits being clear, so in that case,
> discarding the _OSC return buffer is questionable.  There is also no
> reason to return an error and discard the _OSC return buffer if the
> OSC_CAPABILITIES_MASK_ERROR bit is set in it, but printing diagnostic
> messages is appropriate when that happens with OSC_QUERY_ENABLE clear
> in the capabilities buffer.
> 
> Adress this issue by making acpi_run_osc() follow the rules outlined
> above.
> 
> Moreover, make acpi_run_osc() only take the defined _OSC error bits into
> account when checking _OSC errors.
> 
> Link: https://uefi.org/specs/ACPI/6.6/06_Device_Configuration.html#osc-operating-system-capabilities [1]
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>