netdev - Re: [PATCH V4 1/8] drivers/acpi: Add support for Wifi band RF mitigations

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Date: Fri, 23 Jun 2023 11:48:29 -0500
From: "Limonciello, Mario" <mario.limonciello@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Evan Quan <evan.quan@....com>, lenb@...nel.org,
 alexander.deucher@....com, christian.koenig@....com, Xinhui.Pan@....com,
 airlied@...il.com, daniel@...ll.ch, johannes@...solutions.net,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, mdaenzer@...hat.com, maarten.lankhorst@...ux.intel.com,
 tzimmermann@...e.de, hdegoede@...hat.com, jingyuwang_vip@....com,
 lijo.lazar@....com, jim.cromie@...il.com, bellosilicio@...il.com,
 andrealmeid@...lia.com, trix@...hat.com, jsg@....id.au, arnd@...db.de,
 linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
 amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH V4 1/8] drivers/acpi: Add support for Wifi band RF
 mitigations

On 6/23/2023 11:28 AM, Rafael J. Wysocki wrote:
> On Fri, Jun 23, 2023 at 5:57 PM Limonciello, Mario
> <mario.limonciello@....com> wrote:
>>
>> On 6/23/2023 9:52 AM, Rafael J. Wysocki wrote:
>>> On Wed, Jun 21, 2023 at 7:47 AM Evan Quan <evan.quan@....com> wrote:
>>>> From: Mario Limonciello <mario.limonciello@....com>
>>>>
>>>> Due to electrical and mechanical constraints in certain platform designs
>>>> there may be likely interference of relatively high-powered harmonics of
>>>> the (G-)DDR memory clocks with local radio module frequency bands used
>>>> by Wifi 6/6e/7.
>>>>
>>>> To mitigate this, AMD has introduced an ACPI based mechanism that
>>>> devices can use to notify active use of particular frequencies so
>>>> that devices can make relative internal adjustments as necessary
>>>> to avoid this resonance.
>>>>
>>>> In order for a device to support this, the expected flow for device
>>>> driver or subsystems:
>>>>
>>>> Drivers/subsystems contributing frequencies:
>>>>
>>>> 1) During probe, check `wbrf_supported_producer` to see if WBRF supported
>>> The prefix should be acpi_wbrf_ or acpi_amd_wbrf_ even, so it is clear
>>> that this uses ACPI and is AMD-specific.
>> I guess if we end up with an intermediary library approach
>> wbrf_supported_producer makes sense and that could call acpi_wbrf_*.
>>
>> But with no intermediate library your suggestion makes sense.
>>
>> I would prefer not to make it acpi_amd as there is no reason that
>> this exact same problem couldn't happen on an
>> Wifi 6e + Intel SOC + AMD dGPU design too and OEMs could use the
>> same mitigation mechanism as Wifi6e + AMD SOC + AMD dGPU too.
> The mitigation mechanism might be the same, but the AML interface very
> well may be different.

Right.  I suppose right now we should keep it prefixed as "amd",
and if it later is promoted as a standard it can be renamed.

>
> My point is that this particular interface is AMD-specific ATM and I'm
> not aware of any plans to make it "standard" in some way.

Yeah; this implementation is currently AMD specific AML, but I
expect the exact same AML would be delivered to OEMs using the
dGPUs.

>
> Also if the given interface is specified somewhere, it would be good
> to have a pointer to that place.

It's a code first implementation.  I'm discussing with the
owners when they will release it.

>
>>> Whether or not there needs to be an intermediate library wrapped
>>> around this is a different matter.
> IMO individual drivers should not be expected to use this interface
> directly, as that would add to boilerplate code and overall bloat.

The thing is the ACPI method is not a platform method.  It's
a function of the device (_DSM).

The reason for having acpi_wbrf.c in the first place is to
avoid the boilerplate of the _DSM implementation across multiple
drivers.

>
> Also whoever uses it, would first need to check if the device in
> question has an ACPI companion.

Which comes back to Andrew's point.
Either we:

Have a generic wbrf_ helper that takes struct *device and
internally checks if there is an ACPI companion and support.

or

Do the check for support in mac80211 + applicable drivers
and only call the AMD WBRF ACPI method in those drivers in
those cases.