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

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Date:   Fri, 23 Jun 2023 10:57:38 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Evan Quan <evan.quan@....com>
Cc:     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 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.

>
> Whether or not there needs to be an intermediate library wrapped
> around this is a different matter.