ACPI support for System Control and Management Interface (SCMI)

ACPI support for System Control and Management Interface (SCMI)

[Hanjun Guo]

Hi Sudeep,

We are working on the enablement of SCMI for Kunepeng920,
which is a server chip using ACPI, but I didn't see the
ACPI support in the mainline kernel for SCMI.

Kunpeng920 and the upcomming Kunpeng930 have thermal
sensors and other system management features which
needs the SCMI for abstraction layer, do we have plan
to support ACPI for SCMI?

Happy easter!

Thanks
Hanjun


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Re: ACPI support for System Control and Management Interface (SCMI)

[Thanu Rangarajan]

+ Souvik

On 10/04/2020, 07:57, "Hanjun Guo" <guohanjun@huawei.com> wrote:

    Hi Sudeep,

    We are working on the enablement of SCMI for Kunepeng920,
    which is a server chip using ACPI, but I didn't see the
    ACPI support in the mainline kernel for SCMI.

    Kunpeng920 and the upcomming Kunpeng930 have thermal
    sensors and other system management features which
    needs the SCMI for abstraction layer, do we have plan
    to support ACPI for SCMI?

    Happy easter!

    Thanks
    Hanjun



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Re: ACPI support for System Control and Management Interface (SCMI)

[Sudeep Holla]

On Fri, Apr 10, 2020 at 10:26:41AM +0800, Hanjun Guo wrote:
> Hi Sudeep,
>
> We are working on the enablement of SCMI for Kunepeng920,
> which is a server chip using ACPI, but I didn't see the
> ACPI support in the mainline kernel for SCMI.
>
> Kunpeng920 and the upcomming Kunpeng930 have thermal
> sensors and other system management features which
> needs the SCMI for abstraction layer, do we have plan
> to support ACPI for SCMI?
>

Yes and No.

Yes, because the same SCMI compliant firmware needs to work with ACPI as
SCMI is designed so.

No, because we don't plan to add another SCMI layer below ACPI in the
kernel. ACPI specification was extended to support special PCC types
to support the same. IIUC things like sensors are supported using power
meter objects in ACPI and you must be able to use PCC opregion for it or
any custom mechanism to achieve that. However one need to add PCC opregion
handler in Linux. The main idea is you must use existing ACPI methods
and we don't plan to add anything special for SCMI.

SCMI Perf protocol is compatible with CPPC. We can discuss details once
you explore PCC opregion or any alternative you come up with. I am no
ACPI firmware expert and I reckon you may have other interesting ideas.

--
Regards,
Sudeep

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RE: ACPI support for System Control and Management Interface (SCMI)

[Souvik Chakravarty]

> From: Sudeep Holla <sudeep.holla@arm.com>
> Subject: Re: ACPI support for System Control and Management Interface
> (SCMI)
>
> On Fri, Apr 10, 2020 at 10:26:41AM +0800, Hanjun Guo wrote:
> > Hi Sudeep,
> >
> > We are working on the enablement of SCMI for Kunepeng920, which is a
> > server chip using ACPI, but I didn't see the ACPI support in the
> > mainline kernel for SCMI.
> >
> > Kunpeng920 and the upcomming Kunpeng930 have thermal sensors and
> other
> > system management features which needs the SCMI for abstraction layer,
> > do we have plan to support ACPI for SCMI?
> >
>
> Yes and No.
>
> Yes, because the same SCMI compliant firmware needs to work with ACPI as
> SCMI is designed so.
>
> No, because we don't plan to add another SCMI layer below ACPI in the
> kernel. ACPI specification was extended to support special PCC types to
> support the same. IIUC things like sensors are supported using power meter
> objects in ACPI and you must be able to use PCC opregion for it or any
> custom mechanism to achieve that. However one need to add PCC opregion
> handler in Linux. The main idea is you must use existing ACPI methods and
> we don't plan to add anything special for SCMI.

Additionally, if you already have an SCMI compliant firmware that uses Shared Memory based transport, it is compatible with PCC Type 3 Channels in ACPI.

>
> SCMI Perf protocol is compatible with CPPC. We can discuss details once you
> explore PCC opregion or any alternative you come up with. I am no ACPI
> firmware expert and I reckon you may have other interesting ideas.
>
> --
> Regards,
> Sudeep
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Re: ACPI support for System Control and Management Interface (SCMI)

[Hanjun Guo]

Hi Sudeep, Souvik,

On 2020/4/14 20:08, Souvik Chakravarty wrote:
>> From: Sudeep Holla <sudeep.holla@arm.com>
>> Subject: Re: ACPI support for System Control and Management Interface
>> (SCMI)
>>
>> On Fri, Apr 10, 2020 at 10:26:41AM +0800, Hanjun Guo wrote:
>>> Hi Sudeep,
>>>
>>> We are working on the enablement of SCMI for Kunepeng920, which is a
>>> server chip using ACPI, but I didn't see the ACPI support in the
>>> mainline kernel for SCMI.
>>>
>>> Kunpeng920 and the upcomming Kunpeng930 have thermal sensors and
>> other
>>> system management features which needs the SCMI for abstraction layer,
>>> do we have plan to support ACPI for SCMI?
>>>
>>
>> Yes and No.
>>
>> Yes, because the same SCMI compliant firmware needs to work with ACPI as
>> SCMI is designed so.
>>
>> No, because we don't plan to add another SCMI layer below ACPI in the
>> kernel. ACPI specification was extended to support special PCC types to
>> support the same. IIUC things like sensors are supported using power meter
>> objects in ACPI and you must be able to use PCC opregion for it or any
>> custom mechanism to achieve that. However one need to add PCC opregion
>> handler in Linux. The main idea is you must use existing ACPI methods and
>> we don't plan to add anything special for SCMI.
> 
> Additionally, if you already have an SCMI compliant firmware that uses 
> Shared Memory based transport, it is compatible with PCC Type 3 Channels > in ACPI.

We had a disscusion interally (with firmware folks) and this works
for our sensor usecase too, thanks!

> 
>>
>> SCMI Perf protocol is compatible with CPPC. We can discuss details once you
>> explore PCC opregion or any alternative you come up with. I am no ACPI
>> firmware expert and I reckon you may have other interesting ideas.

Sensor works via PCC channels, and SCMI based clock/reset/cpufreq also
have other abstraction level to make it work on ACPI based system,
so for now no more requirements are needed, I will update if we got
new ones :)

Thanks
Hanjun


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