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>
---
 Documentation/driver-api/wbrf.rst | 76 +++++++++++++++++++++++++++++++
 1 file changed, 76 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..52527e76cad4
--- /dev/null
+++ b/Documentation/driver-api/wbrf.rst
@@ -0,0 +1,76 @@
+.. 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` 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.
-- 
2.34.1

On Mon, 30 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@amd.com>
> ---
>  Documentation/driver-api/wbrf.rst | 76 +++++++++++++++++++++++++++++++
>  1 file changed, 76 insertions(+)
>  create mode 100644 Documentation/driver-api/wbrf.rst
> 
> +Driver programming interface
> +============================
> +.. kernel-doc:: drivers/platform/x86/amd/wbrf.c
> +
> +Sample Usage
> +=============

A lot better but you missed adding newlines here for this and previous 
section title.

> +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.

The correct kerneldoc format should be without the closing parenthesis:

1. Text here that
   spills to second line.
2. Second entry.

-- 
 i.

Hi llpo,

Thanks for review, I'll fix the format issue in
the next version.

Regards,
Ma Jun

On 11/20/2023 7:59 PM, Ilpo Järvinen wrote:
> On Mon, 30 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@amd.com>
>> ---
>>  Documentation/driver-api/wbrf.rst | 76 +++++++++++++++++++++++++++++++
>>  1 file changed, 76 insertions(+)
>>  create mode 100644 Documentation/driver-api/wbrf.rst
>>
>> +Driver programming interface
>> +============================
>> +.. kernel-doc:: drivers/platform/x86/amd/wbrf.c
>> +
>> +Sample Usage
>> +=============
> 
> A lot better but you missed adding newlines here for this and previous 
> section title.
> 
>> +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.
> 
> The correct kerneldoc format should be without the closing parenthesis:
> 
> 1. Text here that
>    spills to second line.
> 2. Second entry.
>