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

["Limonciello, Mario" <mario.limonciello@amd.com>]

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@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.
>> 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?