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

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Message-ID: <db2051d0-c847-4d3b-98da-4f4f68a5b30b@redhat.com>
Date:   Mon, 20 Nov 2023 11:35:06 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Ma Jun <Jun.Ma2@....com>, amd-gfx@...ts.freedesktop.org,
        lenb@...nel.org, johannes@...solutions.net, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        alexander.deucher@....com, Lijo.Lazar@....com,
        mario.limonciello@....com
Cc:     majun@....com, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v12 1/9] Documentation/driver-api: Add document about WBRF
 mechanism

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@....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@...hat.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.