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

Johannes Berg
2023-06-21T15:41:20Z

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>
> >
> > 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