linux-kernel - Re: [PATCH v2.1 1/8] ACPI: bus: Fix handling of _OSC errors in acpi_run

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Message-ID: <CAJZ5v0h5gQtPBw-KBrdrSqwmx1qdcv0r3bmXe8h9YqoEd=L5YA@mail.gmail.com>
Date: Tue, 23 Dec 2025 17:13:54 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Linux ACPI <linux-acpi@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, Linux PCI <linux-pci@...r.kernel.org>, 
	Bjorn Helgaas <helgaas@...nel.org>, 
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, Hans de Goede <hansg@...nel.org>, 
	Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH v2.1 1/8] ACPI: bus: Fix handling of _OSC errors in acpi_run_osc()

On Tue, Dec 23, 2025 at 12:12 PM Jonathan Cameron
<jonathan.cameron@...wei.com> wrote:
>
> On Mon, 22 Dec 2025 20:05:44 +0100
> "Rafael J. Wysocki" <rafael@...nel.org> wrote:
>
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.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

Thanks, fixed while applying.

> > 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@...el.com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>

Thank you!

And thanks for all of the reviews!