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| 2 |
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| 3 | =================================
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| 4 | WBRF - Wifi Band RFI Mitigations
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| 5 | =================================
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| 6 |
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| 7 | Due to electrical and mechanical constraints in certain platform designs
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| 8 | there may be likely interference of relatively high-powered harmonics of
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| 9 | the GPU memory clocks with local radio module frequency bands used by
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| 10 | certain Wifi bands.
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| 11 |
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| 12 | To mitigate possible RFI interference producers can advertise the
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| 13 | frequencies in use and consumers can use this information to avoid using
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| 14 | these frequencies for sensitive features.
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| 15 |
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| 16 | When a platform is known to have this issue with any contained devices,
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| 17 | the platform designer will advertise the availability of this feature via
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| 18 | ACPI devices with a device specific method (_DSM).
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| 19 | * Producers with this _DSM will be able to advertise the frequencies in use.
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| 20 | * Consumers with this _DSM will be able to register for notifications of
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| 21 | frequencies in use.
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| 22 |
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| 23 | Some general terms
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| 24 | ==================
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| 25 |
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| 26 | Producer: such component who can produce high-powered radio frequency
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| 27 | Consumer: such component who can adjust its in-use frequency in
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| 28 | response to the radio frequencies of other components to mitigate the
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| 29 | possible RFI.
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| 30 |
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| 31 | To make the mechanism function, those producers should notify active use
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| 32 | of their particular frequencies so that other consumers can make relative
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| 33 | internal adjustments as necessary to avoid this resonance.
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| 34 |
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| 35 | ACPI interface
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| 36 | ==============
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| 37 |
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| 38 | Although initially used by for wifi + dGPU use cases, the ACPI interface
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| 39 | can be scaled to any type of device that a platform designer discovers
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| 40 | can cause interference.
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| 41 |
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| 42 | The GUID used for the _DSM is 7B7656CF-DC3D-4C1C-83E9-66E721DE3070.
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| 43 |
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| 44 | 3 functions are available in this _DSM:
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| 45 |
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| 46 | * 0: discover # of functions available
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| 47 | * 1: record RF bands in use
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| 48 | * 2: retrieve RF bands in use
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| 49 |
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| 50 | Driver programming interface
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| 51 | ============================
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| 52 |
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| 53 | .. kernel-doc:: drivers/platform/x86/amd/wbrf.c
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| 54 |
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| 55 | Sample Usage
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| 56 | =============
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| 57 |
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| 58 | The expected flow for the producers:
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| 59 | 1. During probe, call `acpi_amd_wbrf_supported_producer` to check if WBRF
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| 60 | can be enabled for the device.
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| 61 | 2. On using some frequency band, call `acpi_amd_wbrf_add_remove` with 'add'
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| 62 | param to get other consumers properly notified.
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| 63 | 3. Or on stopping using some frequency band, call
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| 64 | `acpi_amd_wbrf_add_remove` with 'remove' param to get other consumers notified.
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| 65 |
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| 66 | The expected flow for the consumers:
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| 67 | 1. During probe, call `acpi_amd_wbrf_supported_consumer` to check if WBRF
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| 68 | can be enabled for the device.
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| 69 | 2. Call `amd_wbrf_register_notifier` to register for notification
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| 70 | of frequency band change(add or remove) from other producers.
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| 71 | 3. Call the `amd_wbrf_retrieve_freq_band` initially to retrieve
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| 72 | current active frequency bands considering some producers may broadcast
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| 73 | such information before the consumer is up.
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| 74 | 4. On receiving a notification for frequency band change, run
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| 75 | `amd_wbrf_retrieve_freq_band` again to retrieve the latest
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| 76 | active frequency bands.
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| 77 | 5. During driver cleanup, call `amd_wbrf_unregister_notifier` to
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| 78 | unregister the notifier.
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