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

[Limonciello, Mario]

On 6/23/2023 11:28 AM, Rafael J. Wysocki wrote:
> On Fri, Jun 23, 2023 at 5:57 PM Limonciello, Mario
> <mario.limonciello@xxxxxxx> 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@xxxxxxx> wrote:
> > > > From: Mario Limonciello <mario.limonciello@xxxxxxx>
> > > >
> > > > 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.