1.. SPDX-License-Identifier: GPL-2.0-or-later 2 3================================= 4WBRF - Wifi Band RFI Mitigations 5================================= 6 7Due to electrical and mechanical constraints in certain platform designs 8there may be likely interference of relatively high-powered harmonics of 9the GPU memory clocks with local radio module frequency bands used by 10certain Wifi bands. 11 12To mitigate possible RFI interference producers can advertise the 13frequencies in use and consumers can use this information to avoid using 14these frequencies for sensitive features. 15 16When a platform is known to have this issue with any contained devices, 17the platform designer will advertise the availability of this feature via 18ACPI devices with a device specific method (_DSM). 19* Producers with this _DSM will be able to advertise the frequencies in use. 20* Consumers with this _DSM will be able to register for notifications of 21frequencies in use. 22 23Some general terms 24================== 25 26Producer: such component who can produce high-powered radio frequency 27Consumer: such component who can adjust its in-use frequency in 28response to the radio frequencies of other components to mitigate the 29possible RFI. 30 31To make the mechanism function, those producers should notify active use 32of their particular frequencies so that other consumers can make relative 33internal adjustments as necessary to avoid this resonance. 34 35ACPI interface 36============== 37 38Although initially used by for wifi + dGPU use cases, the ACPI interface 39can be scaled to any type of device that a platform designer discovers 40can cause interference. 41 42The GUID used for the _DSM is 7B7656CF-DC3D-4C1C-83E9-66E721DE3070. 43 443 functions are available in this _DSM: 45 46* 0: discover # of functions available 47* 1: record RF bands in use 48* 2: retrieve RF bands in use 49 50Driver programming interface 51============================ 52 53.. kernel-doc:: drivers/platform/x86/amd/wbrf.c 54 55Sample Usage 56============= 57 58The expected flow for the producers: 591. During probe, call `acpi_amd_wbrf_supported_producer` to check if WBRF 60can be enabled for the device. 612. On using some frequency band, call `acpi_amd_wbrf_add_remove` with 'add' 62param to get other consumers properly notified. 633. Or on stopping using some frequency band, call 64`acpi_amd_wbrf_add_remove` with 'remove' param to get other consumers notified. 65 66The expected flow for the consumers: 671. During probe, call `acpi_amd_wbrf_supported_consumer` to check if WBRF 68can be enabled for the device. 692. Call `amd_wbrf_register_notifier` to register for notification 70of frequency band change(add or remove) from other producers. 713. Call the `amd_wbrf_retrieve_freq_band` initally to retrieve 72current active frequency bands considering some producers may broadcast 73such information before the consumer is up. 744. On receiving a notification for frequency band change, run 75`amd_wbrf_retrieve_freq_band` again to retrieve the latest 76active frequency bands. 775. During driver cleanup, call `amd_wbrf_unregister_notifier` to 78unregister the notifier. 79