netdev - Re: [PATCH v14 2/9] platform/x86/amd: Add support for AMD ACPI based Wifi band RFI mitigation feature

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Date: Mon, 4 Dec 2023 14:00:29 +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, 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
Cc: majun@....com, Evan Quan <quanliangl@...mail.com>
Subject: Re: [PATCH v14 2/9] platform/x86/amd: Add support for AMD ACPI based
 Wifi band RFI mitigation feature

Hi,

On 11/29/23 10:13, Ma Jun wrote:
> Due to electrical and mechanical constraints in certain platform designs
> there may be likely interference of relatively high-powered harmonics of
> the (G-)DDR memory clocks with local radio module frequency bands used
> by Wifi 6/6e/7.
> 
> To mitigate this, AMD has introduced a mechanism that devices can use to
> notify active use of particular frequencies so that other devices can make
> relative internal adjustments as necessary to avoid this resonance.
> 
> Co-developed-by: Evan Quan <quanliangl@...mail.com>
> Signed-off-by: Evan Quan <quanliangl@...mail.com>
> Signed-off-by: Ma Jun <Jun.Ma2@....com>
> 
> --
> v11:
>  - fix typo(Simon)
> v12:
>  - Fix the code logic (Rafael)
>  - Move amd_wbrf.c to drivers/platform/x86/amd/wbrf.c
>  - Updated Evan's email because he's no longer at AMD.Thanks
> for his work in earlier versions.
> v13:
>  - Fix the format issue (IIpo Jarvinen)
>  - Add comment for some functions
> v14:
>  - Use the apci_check_dsm and acpi_evaluate_dsm (Hans de Goede)

Thank you this is much better.

I notice that the #define ACPI_AMD_WBRF_METHOD	"\\WBRF"
still exists though and that this is still used in
static bool acpi_amd_wbrf_supported_system(void).

I think it might be better to just remove
these 2 all together.

Checking if a DSM with the expected GUID is present
and if that has the correct bits set in its supported
mask should be enough.

And on future systems the implementer may decide to
not have a WBRF helper function at all and instead
handle everything in the _DSM method.

So the "\\WBRF" check seems to be checking for
what really is an implementation detail.

2 other very small remarks:

> +/**
> + * acpi_amd_wbrf_supported_producer - determine if the WBRF can be enabled
> + *                                    for the device as a producer
> + *
> + * @dev: device pointer
> + *
> + * Check if the platform equipped with necessary implementations to
> + * support WBRF for the device as a producer.
> + *
> + * Return:
> + * true if WBRF is supported, otherwise returns false
> + */
> +bool acpi_amd_wbrf_supported_producer(struct device *dev)
> +{
> +	struct acpi_device *adev;
> +
> +	adev = ACPI_COMPANION(dev);
> +	if (!adev)
> +		return false;
> +
> +	if (!acpi_amd_wbrf_supported_system())
> +		return false;
> +
> +
> +	return acpi_check_dsm(adev->handle, &wifi_acpi_dsm_guid,
> +			      WBRF_REVISION, BIT(WBRF_RECORD));
> +}
> +EXPORT_SYMBOL_GPL(acpi_amd_wbrf_supported_producer);

Please don't use double empty lines, one empty line to separate things
is enough.

> +
> +/**
> + * acpi_amd_wbrf_supported_consumer - determine if the WBRF can be enabled
> + *                                    for the device as a consumer
> + *
> + * @dev: device pointer
> + *
> + * Determine if the platform equipped with necessary implementations to
> + * support WBRF for the device as a consumer.
> + *
> + * Return:
> + * true if WBRF is supported, otherwise returns false.
> + */
> +bool acpi_amd_wbrf_supported_consumer(struct device *dev)
> +{
> +	struct acpi_device *adev;
> +
> +	adev = ACPI_COMPANION(dev);
> +	if (!adev)
> +		return false;
> +
> +	if (!acpi_amd_wbrf_supported_system())
> +		return false;
> +
> +	return acpi_check_dsm(adev->handle, &wifi_acpi_dsm_guid,
> +			      WBRF_REVISION, BIT(WBRF_RETRIEVE));
> +}
> +EXPORT_SYMBOL_GPL(acpi_amd_wbrf_supported_consumer);
> +
> +/**
> + * amd_wbrf_retrieve_freq_band - retrieve current active frequency
> + *                                     bands

You may go a bit over the 80 chars limit, please just make this
a single line:

 * amd_wbrf_retrieve_freq_band - retrieve current active frequency bands

> + *
> + * @dev: device pointer
> + * @out: output structure containing all the active frequency bands
> + *
> + * Retrieve the current active frequency bands which were broadcasted
> + * by other producers. The consumer who calls this API should take
> + * proper actions if any of the frequency band may cause RFI with its
> + * own frequency band used.
> + *
> + * Return:
> + * 0 for getting wifi freq band successfully.
> + * Returns a negative error code for failure.
> + */

Regards,

Hans