[PATCH v14 1/9] Documentation/driver-api: Add document about WBRF mechanism

[Mario Limonciello]

On 11/29/2023 03:13, Ma Jun wrote:
> 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 at amd.com>
> Reviewed-by: Hans de Goede <hdegoede at redhat.com>

Reviewed-by: Mario Limonciello <mario.limonciello at amd.com>

> 
> --
> v14:
> - Fix the format issue (IIpo Jarvinen)
> ---
>   Documentation/driver-api/wbrf.rst | 78 +++++++++++++++++++++++++++++++
>   1 file changed, 78 insertions(+)
>   create mode 100644 Documentation/driver-api/wbrf.rst
> 
> diff --git a/Documentation/driver-api/wbrf.rst b/Documentation/driver-api/wbrf.rst
> new file mode 100644
> index 000000000000..12793bb1abce
> --- /dev/null
> +++ b/Documentation/driver-api/wbrf.rst
> @@ -0,0 +1,78 @@
> +.. SPDX-License-Identifier: GPL-2.0-or-later
> +
> +=================================
> +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
> +============================
> +
> +.. kernel-doc:: drivers/platform/x86/amd/wbrf.c
> +
> +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.