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

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Date: Wed, 21 Jun 2023 17:39:41 +0200
From: Johannes Berg <johannes@...solutions.net>
To: Andrew Lunn <andrew@...n.ch>, Evan Quan <evan.quan@....com>
Cc: rafael@...nel.org, lenb@...nel.org, alexander.deucher@....com, 
 christian.koenig@....com, Xinhui.Pan@....com, airlied@...il.com,
 daniel@...ll.ch,  davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com,  mario.limonciello@....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 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@....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.
> 
> Do only ACPI based systems have:
> 
>    interference of relatively high-powered harmonics of the (G-)DDR
>    memory clocks with local radio module frequency bands used by
>    Wifi 6/6e/7."
> 
> 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 supported.
> > + * 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);
> 
> 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