[PATCH v12 1/9] Documentation/driver-api: Add document about WBRF mechanism

[Ma, Jun]

Hi llpo,

Thanks for these comments on format issues, I'll
fix it in the next version.

Regards,
Ma Jun

On 10/17/2023 5:20 PM, Ilpo Järvinen wrote:
> On Tue, 17 Oct 2023, 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>
>> ---
>>  Documentation/driver-api/wbrf.rst | 73 +++++++++++++++++++++++++++++++
>>  1 file changed, 73 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..8561840263b3
>> --- /dev/null
>> +++ b/Documentation/driver-api/wbrf.rst
>> @@ -0,0 +1,73 @@
>> +.. SPDX-License-Identifier: GPL-2.0-or-later
>> +
>> +=================================
>> +WBRF - Wifi Band RFI Mitigations
>> +=================================
>> +Due to electrical and mechanical constraints in certain platform designs
> 
> Add empty line before starting the content of a section.
> 
>> +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` intentionally 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.
> 
> Align these so that only the numbers start from first column. I think the 
> proper markup for numbered lists is 1. not 1).
> 
>