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¶
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int acpi_amd_wbrf_add_remove(struct device *dev, uint8_t action, struct wbrf_ranges_in_out *in)¶
add or remove the frequency band the device is using
Parameters
struct device *devdevice pointer
uint8_t actionremove or add the frequency band into bios
struct wbrf_ranges_in_out *ininput structure containing the frequency band the device is using
Description
Broadcast to other consumers the frequency band the device starts to use. Underneath the surface the information is cached into an internal buffer first. Then a notification is sent to all those registered consumers. So then they can retrieve that buffer to know the latest active frequency bands. Consumers that haven’t yet been registered can retrieve the information from the cache when they register.
Return
0 for success add/remove wifi frequency band. Returns a negative error code for failure.
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bool acpi_amd_wbrf_supported_producer(struct device *dev)¶
determine if the WBRF can be enabled for the device as a producer
Parameters
struct device *devdevice pointer
Description
Check if the platform equipped with necessary implementations to support WBRF for the device as a producer.
Return
true if WBRF is supported, otherwise returns false
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bool acpi_amd_wbrf_supported_consumer(struct device *dev)¶
determine if the WBRF can be enabled for the device as a consumer
Parameters
struct device *devdevice pointer
Description
Determine if the platform equipped with necessary implementations to support WBRF for the device as a consumer.
Return
true if WBRF is supported, otherwise returns false.
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int amd_wbrf_retrieve_freq_band(struct device *dev, struct wbrf_ranges_in_out *out)¶
retrieve current active frequency bands
Parameters
struct device *devdevice pointer
struct wbrf_ranges_in_out *outoutput structure containing all the active frequency bands
Description
Retrieve the current active frequency bands which were broadcasted by other producers. The consumer who calls this API should take proper actions if any of the frequency band may cause RFI with its own frequency band used.
Return
0 for getting wifi freq band successfully. Returns a negative error code for failure.
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int amd_wbrf_register_notifier(struct notifier_block *nb)¶
register for notifications of frequency band update
Parameters
struct notifier_block *nbdriver notifier block
Description
The consumer should register itself via this API so that it can get notified on the frequency band updates from other producers.
Return
0 for registering a consumer driver successfully. Returns a negative error code for failure.
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int amd_wbrf_unregister_notifier(struct notifier_block *nb)¶
unregister for notifications of frequency band update
Parameters
struct notifier_block *nbdriver notifier block
Description
The consumer should call this API when it is longer interested with the frequency band updates from other producers. Usually, this should be performed during driver cleanup.
Return
0 for unregistering a consumer driver. Returns a negative error code for failure.
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 initally 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.