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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@amd.com> Reviewed-by: Hans de Goede <hdegoede@redhat.com> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
79 lines
3.0 KiB
ReStructuredText
79 lines
3.0 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-or-later
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=================================
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WBRF - Wifi Band RFI Mitigations
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=================================
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Due to electrical and mechanical constraints in certain platform designs
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there may be likely interference of relatively high-powered harmonics of
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the GPU memory clocks with local radio module frequency bands used by
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certain Wifi bands.
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To mitigate possible RFI interference producers can advertise the
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frequencies in use and consumers can use this information to avoid using
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these frequencies for sensitive features.
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When a platform is known to have this issue with any contained devices,
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the platform designer will advertise the availability of this feature via
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ACPI devices with a device specific method (_DSM).
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* Producers with this _DSM will be able to advertise the frequencies in use.
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* Consumers with this _DSM will be able to register for notifications of
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frequencies in use.
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Some general terms
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==================
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Producer: such component who can produce high-powered radio frequency
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Consumer: such component who can adjust its in-use frequency in
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response to the radio frequencies of other components to mitigate the
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possible RFI.
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To make the mechanism function, those producers should notify active use
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of their particular frequencies so that other consumers can make relative
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internal adjustments as necessary to avoid this resonance.
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ACPI interface
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==============
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Although initially used by for wifi + dGPU use cases, the ACPI interface
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can be scaled to any type of device that a platform designer discovers
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can cause interference.
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The GUID used for the _DSM is 7B7656CF-DC3D-4C1C-83E9-66E721DE3070.
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3 functions are available in this _DSM:
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* 0: discover # of functions available
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* 1: record RF bands in use
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* 2: retrieve RF bands in use
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Driver programming interface
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============================
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.. kernel-doc:: drivers/platform/x86/amd/wbrf.c
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Sample Usage
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=============
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The expected flow for the producers:
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1. During probe, call `acpi_amd_wbrf_supported_producer` to check if WBRF
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can be enabled for the device.
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2. On using some frequency band, call `acpi_amd_wbrf_add_remove` with 'add'
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param to get other consumers properly notified.
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3. Or on stopping using some frequency band, call
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`acpi_amd_wbrf_add_remove` with 'remove' param to get other consumers notified.
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The expected flow for the consumers:
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1. During probe, call `acpi_amd_wbrf_supported_consumer` to check if WBRF
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can be enabled for the device.
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2. Call `amd_wbrf_register_notifier` to register for notification
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of frequency band change(add or remove) from other producers.
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3. Call the `amd_wbrf_retrieve_freq_band` initally to retrieve
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current active frequency bands considering some producers may broadcast
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such information before the consumer is up.
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4. On receiving a notification for frequency band change, run
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`amd_wbrf_retrieve_freq_band` again to retrieve the latest
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active frequency bands.
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5. During driver cleanup, call `amd_wbrf_unregister_notifier` to
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unregister the notifier.
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