.. SPDX-License-Identifier: GPL-2.0-or-later

================================= WBRF - Wifi Band RFI Mitigations

Due to electrical and mechanical constraints in certain platform designs there may be likely interference of relatively high-powered harmonics of the GPU memory clocks with local radio module frequency bands used by certain Wifi bands.

To mitigate possible RFI interference producers can advertise the frequencies in use and consumers can use this information to avoid using these frequencies for sensitive features.

When a platform is known to have this issue with any contained devices, the platform designer will advertise the availability of this feature via ACPI devices with a device specific method (_DSM).

• Producers with this _DSM will be able to advertise the frequencies in use.
• Consumers with this _DSM will be able to register for notifications of frequencies in use.

Some general terms

Producer: such component who can produce high-powered radio frequency Consumer: such component who can adjust its in-use frequency in response to the radio frequencies of other components to mitigate the possible RFI.

To make the mechanism function, those producers should notify active use of their particular frequencies so that other consumers can make relative internal adjustments as necessary to avoid this resonance.

ACPI interface

Although initially used by for wifi + dGPU use cases, the ACPI interface can be scaled to any type of device that a platform designer discovers can cause interference.

The GUID used for the _DSM is 7B7656CF-DC3D-4C1C-83E9-66E721DE3070.

3 functions are available in this _DSM:

• 0: discover # of functions available
• 1: record RF bands in use
• 2: retrieve RF bands in use

Driver programming interface

.. kernel-doc:: drivers/platform/x86/amd/wbrf.c

Sample Usage

The expected flow for the producers:

1. During probe, call acpi_amd_wbrf_supported_producer to check if WBRF can be enabled for the device.
2. On using some frequency band, call acpi_amd_wbrf_add_remove with 'add' param to get other consumers properly notified.
3. Or on stopping using some frequency band, call acpi_amd_wbrf_add_remove with 'remove' param to get other consumers notified.

The expected flow for the consumers:

1. During probe, call acpi_amd_wbrf_supported_consumer to check if WBRF can be enabled for the device.
2. Call amd_wbrf_register_notifier to register for notification of frequency band change(add or remove) from other producers.
3. Call the amd_wbrf_retrieve_freq_band initially to retrieve current active frequency bands considering some producers may broadcast such information before the consumer is up.
4. On receiving a notification for frequency band change, run amd_wbrf_retrieve_freq_band again to retrieve the latest active frequency bands.
5. During driver cleanup, call amd_wbrf_unregister_notifier to unregister the notifier.