[v2] ACPI: CPPC: Don't require _OSC if X86_FEATURE_CPPC is supported

[PATCH v2] ACPI: CPPC: Don't require _OSC if X86_FEATURE_CPPC is supported

Posted by Mario Limonciello 3 years, 9 months ago

commit 72f2ecb7ece7 ("ACPI: bus: Set CPPC _OSC bits for all and
when CPPC_LIB is supported") added support for claiming to
support CPPC in _OSC on non-Intel platforms.

This unfortunately caused a regression on a vartiety of AMD
platforms in the field because a number of AMD platforms don't set
the `_OSC` bit 5 or 6 to indicate CPPC or CPPC v2 support.

As these AMD platforms already claim CPPC support via a dedicated
MSR from `X86_FEATURE_CPPC`, use that to enable this feature rather
than requiring the `_OSC` on platforms with a dedicated MSR.

If there is additional breakage on the shared memory designs also
missing this _OSC, additional follow up changes may be needed.

Fixes: 72f2ecb7ece7 ("Set CPPC _OSC bits for all and when CPPC_LIB is supported")
Reported-by: Perry Yuan <perry.yuan@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
v1->v2:
 * Make the code easier to follow (suggested by Rafael)
 * Update commit message to reflect this is only fixing the MSR case
   and that any other breakage from 72f2ecb7ece7 will need additional
   follow ups
 drivers/acpi/cppc_acpi.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 903528f7e187..cc154519c608 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -629,7 +629,15 @@ static bool is_cppc_supported(int revision, int num_ent)
 		return false;
 	}
 
-	return true;
+	if (!osc_sb_cppc_not_supported)
+		return true;
+
+	pr_debug("Firmware missing _OSC support\n");
+#ifdef CONFIG_X86
+	return boot_cpu_has(X86_FEATURE_CPPC);
+#else
+	return false;
+#endif
 }
 
 /*
@@ -684,9 +692,6 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
 	acpi_status status;
 	int ret = -ENODATA;
 
-	if (osc_sb_cppc_not_supported)
-		return -ENODEV;
-
 	/* Parse the ACPI _CPC table for this CPU. */
 	status = acpi_evaluate_object_typed(handle, "_CPC", NULL, &output,
 			ACPI_TYPE_PACKAGE);
-- 
2.25.1

Re: [PATCH v2] ACPI: CPPC: Don't require _OSC if X86_FEATURE_CPPC is supported

Posted by Rafael J. Wysocki 3 years, 9 months ago

On Wed, Jun 29, 2022 at 10:04 PM Mario Limonciello
<mario.limonciello@amd.com> wrote:
>
> commit 72f2ecb7ece7 ("ACPI: bus: Set CPPC _OSC bits for all and
> when CPPC_LIB is supported") added support for claiming to
> support CPPC in _OSC on non-Intel platforms.
>
> This unfortunately caused a regression on a vartiety of AMD
> platforms in the field because a number of AMD platforms don't set
> the `_OSC` bit 5 or 6 to indicate CPPC or CPPC v2 support.
>
> As these AMD platforms already claim CPPC support via a dedicated
> MSR from `X86_FEATURE_CPPC`, use that to enable this feature rather
> than requiring the `_OSC` on platforms with a dedicated MSR.
>
> If there is additional breakage on the shared memory designs also
> missing this _OSC, additional follow up changes may be needed.
>
> Fixes: 72f2ecb7ece7 ("Set CPPC _OSC bits for all and when CPPC_LIB is supported")
> Reported-by: Perry Yuan <perry.yuan@amd.com>
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>

I'm still concerned about the possible cases in which there is _CPC,
but it returns garbage, because the firmware thinks that the OS will
not use _CPC due to the _OSC handshake.

> ---
> v1->v2:
>  * Make the code easier to follow (suggested by Rafael)
>  * Update commit message to reflect this is only fixing the MSR case
>    and that any other breakage from 72f2ecb7ece7 will need additional
>    follow ups
>  drivers/acpi/cppc_acpi.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 903528f7e187..cc154519c608 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -629,7 +629,15 @@ static bool is_cppc_supported(int revision, int num_ent)
>                 return false;
>         }
>
> -       return true;
> +       if (!osc_sb_cppc_not_supported)
> +               return true;
> +
> +       pr_debug("Firmware missing _OSC support\n");
> +#ifdef CONFIG_X86
> +       return boot_cpu_has(X86_FEATURE_CPPC);

So can you please add an additional X86_VENDOR_AMD check to the above?

> +#else
> +       return false;
> +#endif
>  }
>
>  /*
> @@ -684,9 +692,6 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
>         acpi_status status;
>         int ret = -ENODATA;
>
> -       if (osc_sb_cppc_not_supported)
> -               return -ENODEV;
> -
>         /* Parse the ACPI _CPC table for this CPU. */
>         status = acpi_evaluate_object_typed(handle, "_CPC", NULL, &output,
>                         ACPI_TYPE_PACKAGE);
> --
> 2.25.1
>

RE: [PATCH v2] ACPI: CPPC: Don't require _OSC if X86_FEATURE_CPPC is supported

Posted by Limonciello, Mario 3 years, 9 months ago

[Public]



> -----Original Message-----
> From: Rafael J. Wysocki <rafael@kernel.org>
> Sent: Tuesday, July 5, 2022 13:12
> To: Limonciello, Mario <Mario.Limonciello@amd.com>
> Cc: Rafael J. Wysocki <rafael@kernel.org>; Len Brown <lenb@kernel.org>;
> Sudeep Holla <sudeep.holla@arm.com>; Pierre Gondois
> <pierre.gondois@arm.com>; Yuan, Perry <Perry.Yuan@amd.com>; ACPI
> Devel Maling List <linux-acpi@vger.kernel.org>; Linux Kernel Mailing List
> <linux-kernel@vger.kernel.org>
> Subject: Re: [PATCH v2] ACPI: CPPC: Don't require _OSC if
> X86_FEATURE_CPPC is supported
> 
> On Wed, Jun 29, 2022 at 10:04 PM Mario Limonciello
> <mario.limonciello@amd.com> wrote:
> >
> > commit 72f2ecb7ece7 ("ACPI: bus: Set CPPC _OSC bits for all and
> > when CPPC_LIB is supported") added support for claiming to
> > support CPPC in _OSC on non-Intel platforms.
> >
> > This unfortunately caused a regression on a vartiety of AMD
> > platforms in the field because a number of AMD platforms don't set
> > the `_OSC` bit 5 or 6 to indicate CPPC or CPPC v2 support.
> >
> > As these AMD platforms already claim CPPC support via a dedicated
> > MSR from `X86_FEATURE_CPPC`, use that to enable this feature rather
> > than requiring the `_OSC` on platforms with a dedicated MSR.
> >
> > If there is additional breakage on the shared memory designs also
> > missing this _OSC, additional follow up changes may be needed.
> >
> > Fixes: 72f2ecb7ece7 ("Set CPPC _OSC bits for all and when CPPC_LIB is
> supported")
> > Reported-by: Perry Yuan <perry.yuan@amd.com>
> > Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> 
> I'm still concerned about the possible cases in which there is _CPC,
> but it returns garbage, because the firmware thinks that the OS will
> not use _CPC due to the _OSC handshake.
> 
> > ---
> > v1->v2:
> >  * Make the code easier to follow (suggested by Rafael)
> >  * Update commit message to reflect this is only fixing the MSR case
> >    and that any other breakage from 72f2ecb7ece7 will need additional
> >    follow ups
> >  drivers/acpi/cppc_acpi.c | 13 +++++++++----
> >  1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> > index 903528f7e187..cc154519c608 100644
> > --- a/drivers/acpi/cppc_acpi.c
> > +++ b/drivers/acpi/cppc_acpi.c
> > @@ -629,7 +629,15 @@ static bool is_cppc_supported(int revision, int
> num_ent)
> >                 return false;
> >         }
> >
> > -       return true;
> > +       if (!osc_sb_cppc_not_supported)
> > +               return true;
> > +
> > +       pr_debug("Firmware missing _OSC support\n");
> > +#ifdef CONFIG_X86
> > +       return boot_cpu_has(X86_FEATURE_CPPC);
> 
> So can you please add an additional X86_VENDOR_AMD check to the above?

Very well, I'll send out v4 shortly with that modification.

> 
> > +#else
> > +       return false;
> > +#endif
> >  }
> >
> >  /*
> > @@ -684,9 +692,6 @@ int acpi_cppc_processor_probe(struct
> acpi_processor *pr)
> >         acpi_status status;
> >         int ret = -ENODATA;
> >
> > -       if (osc_sb_cppc_not_supported)
> > -               return -ENODEV;
> > -
> >         /* Parse the ACPI _CPC table for this CPU. */
> >         status = acpi_evaluate_object_typed(handle, "_CPC", NULL, &output,
> >                         ACPI_TYPE_PACKAGE);
> > --
> > 2.25.1
> >