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

[Limonciello, Mario]

On 6/21/2023 11:52 AM, Andrew Lunn wrote:
> On Wed, Jun 21, 2023 at 11:15:00AM -0500, Limonciello, Mario wrote:
> > On 6/21/2023 10:39 AM, Johannes Berg wrote:
> > > 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@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.
> > > > 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.
> > The way that WBRF has been architected, it's intended to be able
> > to scale to any type of device pair that has harmonic issues.
> So you set out to make something generic...
>
> > In the first use (Wifi 6e + specific AMD dGPUs) that matches this
> > series BIOS has the following purposes:
> >
> > 1) The existence of _DSM indicates that the system may not have
> > adequate shielding and should be using these mitigations.
> >
> > 2) Notification mechanism of frequency use.
> >
> > For the first problematic devices we *could* have done notifications
> > entirely in native Linux kernel code with notifier chains.
> > However that still means you need a hint from the platform that the
> > functionality is needed like a _DSD bit.
> >
> > It's also done this way so that AML could do some of the notifications
> > directly to applicable devices in the future without needing "consumer"
> > driver participation.
> And then tie is very closely to ACPI.
>
> Now, you are AMD, i get that ACPI is what you have. But i think as
> kernel Maintainers, we need to consider that ACPI is not the only
> thing used. Do we want the APIs to be agnostic? I think APIs used by
> drivers should be agnostic.
>
>        Andrew
I think what you're asking for is another layer of indirection
like CONFIG_WBRF in addition to CONFIG_ACPI_WBRF.

Producers would call functions like wbrf_supported_producer()
where the source file is not guarded behind CONFIG_ACPI_WBRF,
but instead by CONFIG_WBRF and locally use CONFIG_ACPI_WBRF within
it.  So a producer could look like this:

bool wbrf_supported_producer(struct device *dev)
{
#ifdef CONFIG_ACPI_WBRF
    struct acpi_device *adev = ACPI_COMPANION(dev);

    if (adev)
        return check_acpi_wbrf(adev->handle,
                       WBRF_REVISION,
                       1ULL << WBRF_RECORD);
#endif
    return -ENODEV;

}
EXPORT_SYMBOL_GPL(wbrf_supported_producer);

And then adding/removing could look something like this

int wbrf_add_exclusion(struct device *dev,
               struct wbrf_ranges_in *in)
{
#ifdef CONFIG_ACPI_WBRF
    struct acpi_device *adev = ACPI_COMPANION(dev);

    if (adev)
        return wbrf_record(adev, WBRF_RECORD_ADD, in);
#endif
    return -ENODEV;
}
EXPORT_SYMBOL_GPL(wbrf_add_exclusion);

int wbrf_remove_exclusion(struct device *dev,
               struct wbrf_ranges_in *in)
{
#ifdef CONFIG_ACPI_WBRF
    struct acpi_device *adev = ACPI_COMPANION(dev);

    if (adev)
        return wbrf_record(adev, WBRF_RECORD_REMOVE, in);
#endif
    return -ENODEV;
}
EXPORT_SYMBOL_GPL(wbrf_remove_exclusion);

This would allow anyone interested in making a non-ACPI implementation
be able to slide it into those functions.

How does that sound?