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    SubjectRe: [PATCH v12 1/9] Documentation/driver-api: Add document about WBRF mechanism
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    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@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
    > +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@redhat.com>

    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.

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