1 .. SPDX-License-Identifier: GPL-2.0-or-later 2 3 ================================= 4 WBRF - Wifi Band RFI Mitigations 5 ================================= 6 7 Due to electrical and mechanical constraints in certain platform designs 8 there may be likely interference of relatively high-powered harmonics of 9 the GPU memory clocks with local radio module frequency bands used by 10 certain Wifi bands. 11 12 To mitigate possible RFI interference producers can advertise the 13 frequencies in use and consumers can use this information to avoid using 14 these frequencies for sensitive features. 15 16 When a platform is known to have this issue with any contained devices, 17 the platform designer will advertise the availability of this feature via 18 ACPI 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 21 frequencies in use. 22 23 Some general terms 24 ================== 25 26 Producer: such component who can produce high-powered radio frequency 27 Consumer: such component who can adjust its in-use frequency in 28 response to the radio frequencies of other components to mitigate the 29 possible RFI. 30 31 To make the mechanism function, those producers should notify active use 32 of their particular frequencies so that other consumers can make relative 33 internal adjustments as necessary to avoid this resonance. 34 35 ACPI interface 36 ============== 37 38 Although initially used by for wifi + dGPU use cases, the ACPI interface 39 can be scaled to any type of device that a platform designer discovers 40 can cause interference. 41 42 The GUID used for the _DSM is 7B7656CF-DC3D-4C1C-83E9-66E721DE3070. 43 44 3 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 50 Driver programming interface 51 ============================ 52 53 .. kernel-doc:: drivers/platform/x86/amd/wbrf.c 54 55 Sample Usage 56 ============= 57 58 The expected flow for the producers: 59 1. During probe, call `acpi_amd_wbrf_supported_producer` to check if WBRF 60 can be enabled for the device. 61 2. On using some frequency band, call `acpi_amd_wbrf_add_remove` with 'add' 62 param to get other consumers properly notified. 63 3. Or on stopping using some frequency band, call 64 `acpi_amd_wbrf_add_remove` with 'remove' param to get other consumers notified. 65 66 The expected flow for the consumers: 67 1. During probe, call `acpi_amd_wbrf_supported_consumer` to check if WBRF 68 can be enabled for the device. 69 2. Call `amd_wbrf_register_notifier` to register for notification 70 of frequency band change(add or remove) from other producers. 71 3. Call the `amd_wbrf_retrieve_freq_band` initially to retrieve 72 current active frequency bands considering some producers may broadcast 73 such information before the consumer is up. 74 4. On receiving a notification for frequency band change, run 75 `amd_wbrf_retrieve_freq_band` again to retrieve the latest 76 active frequency bands. 77 5. During driver cleanup, call `amd_wbrf_unregister_notifier` to 78 unregister the notifier.
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