Hi, On 10/17/23 04:53, 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@xxxxxxx> > --- > 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 > +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. "intentionally" in this sentence should be "initially" (I presume). With that fixed and Ilpo's review comments addressed you may add my: Reviewed-by: Hans de Goede <hdegoede@xxxxxxxxxx> to this patch. Regards, Hans > +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.
