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Subject: Re: [PATCH V4 1/8] drivers/acpi: Add support for Wifi band RF
 mitigations
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Andrew Lunn <andrew@lunn.ch>, Evan Quan <evan.quan@amd.com>
Cc:     rafael@kernel.org, lenb@kernel.org, alexander.deucher@amd.com,
        christian.koenig@amd.com, Xinhui.Pan@amd.com, airlied@gmail.com,
        daniel@ffwll.ch, davem@davemloft.net, edumazet@google.com,
        kuba@kernel.org, pabeni@redhat.com, mario.limonciello@amd.com,
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        tzimmermann@suse.de, hdegoede@redhat.com, jingyuwang_vip@163.com,
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        andrealmeid@igalia.com, trix@redhat.com, jsg@jsg.id.au,
        arnd@arndb.de, linux-kernel@vger.kernel.org,
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        netdev@vger.kernel.org
Date:   Wed, 21 Jun 2023 17:39:41 +0200
In-Reply-To: <3a7c8ffa-de43-4795-ae76-5cd9b00c52b5@lunn.ch>
References: <20230621054603.1262299-1-evan.quan@amd.com>
         <20230621054603.1262299-2-evan.quan@amd.com>
         <3a7c8ffa-de43-4795-ae76-5cd9b00c52b5@lunn.ch>
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On Wed, 2023-06-21 at 17:36 +0200, Andrew Lunn wrote:
> On Wed, Jun 21, 2023 at 01:45:56PM +0800, Evan Quan wrote:
> > From: Mario Limonciello <mario.limonciello@amd.com>
> >=20
> > Due to electrical and mechanical constraints in certain platform design=
s
> > there may be likely interference of relatively high-powered harmonics o=
f
> > the (G-)DDR memory clocks with local radio module frequency bands used
> > by Wifi 6/6e/7.
> >=20
> > 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.
>=20
> Do only ACPI based systems have:
>=20
>    interference of relatively high-powered harmonics of the (G-)DDR
>    memory clocks with local radio module frequency bands used by
>    Wifi 6/6e/7."
>=20
> Could Device Tree based systems not experience this problem?

They could, of course, but they'd need some other driver to change
_something_ in the system? I don't even know what this is doing
precisely under the hood in the ACPI BIOS, perhaps it adjusts the DDR
memory clock frequency in response to WiFi using a frequency that will
cause interference with harmonics.


> > +/**
> > + * APIs needed by drivers/subsystems for contributing frequencies:
> > + * During probe, check `wbrf_supported_producer` to see if WBRF is sup=
ported.
> > + * If adding frequencies, then call `wbrf_add_exclusion` with the
> > + * start and end points specified for the frequency ranges added.
> > + * If removing frequencies, then call `wbrf_remove_exclusion` with
> > + * start and end points specified for the frequency ranges added.
> > + */
> > +bool wbrf_supported_producer(struct acpi_device *adev);
> > +int wbrf_add_exclusion(struct acpi_device *adev,
> > +		       struct wbrf_ranges_in *in);
> > +int wbrf_remove_exclusion(struct acpi_device *adev,
> > +			  struct wbrf_ranges_in *in);
>=20
> Could struct device be used here, to make the API agnostic to where
> the information is coming from? That would then allow somebody in the
> future to implement a device tree based information provider.

That does make sense, and it wouldn't even be that much harder if we
assume in a given platform there's only one provider - but once you go
beyond that these would need to call function pointers I guess? Though
that could be left for "future improvement" too.

johannes