Add documentation about AMD's Wifi band RFI mitigation (WBRF) mechanism explaining the theory and how it is used. Signed-off-by: Ma Jun <Jun.Ma2@xxxxxxx> --- Documentation/driver-api/wbrf.rst | 73 +++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) create mode 100644 Documentation/driver-api/wbrf.rst diff --git a/Documentation/driver-api/wbrf.rst b/Documentation/driver-api/wbrf.rst new file mode 100644 index 000000000000..8561840263b3 --- /dev/null +++ b/Documentation/driver-api/wbrf.rst @@ -0,0 +1,73 @@ +.. 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` intentionally 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. -- 2.34.1
