Re: [PATCH v12 2/9] platform/x86/amd: Add support for AMD ACPI based Wifi band RFI mitigation feature

[Hans de Goede]

Hi,

On 10/17/23 04:53, 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@xxxxxxxxxxx>
> Signed-off-by: Evan Quan <quanliangl@xxxxxxxxxxx>
> Signed-off-by: Ma Jun <Jun.Ma2@xxxxxxx>

<snip>

> +bool acpi_amd_wbrf_supported_producer(struct device *dev)
> +{
> +	struct acpi_device *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);

So until here you use acpi_dsm methods (1), which matches
with patch 1/9 which says that both producers and consumers
use a _DSM for WBRF.

1) With the exception of the weird acpi_amd_wbrf_supported_system()
helper.

> +static union acpi_object *
> +acpi_evaluate_wbrf(acpi_handle handle, u64 rev, u64 func)
> +{
> +	acpi_status ret;
> +	struct acpi_buffer buf = {ACPI_ALLOCATE_BUFFER, NULL};
> +	union acpi_object params[4];
> +	struct acpi_object_list input = {
> +		.count = 4,
> +		.pointer = params,
> +	};
> +
> +	params[0].type = ACPI_TYPE_INTEGER;
> +	params[0].integer.value = rev;
> +	params[1].type = ACPI_TYPE_INTEGER;
> +	params[1].integer.value = func;
> +	params[2].type = ACPI_TYPE_PACKAGE;
> +	params[2].package.count = 0;
> +	params[2].package.elements = NULL;
> +	params[3].type = ACPI_TYPE_STRING;
> +	params[3].string.length = 0;
> +	params[3].string.pointer = NULL;
> +
> +	ret = acpi_evaluate_object(handle, "WBRF", &input, &buf);
> +	if (ACPI_FAILURE(ret))
> +		return NULL;
> +
> +	return buf.pointer;
> +}

But now all of a sudden you start calling a WBRF method
directly instead of calling a _DSM by GUID, which seems
to be intended for consumers.

This contradicts with the documentation which says that
consumers also use the _DSM.

And this looks a lot like acpi_evaluate_dsm and
... (continued below)

> +
> +static bool check_acpi_wbrf(acpi_handle handle, u64 rev, u64 funcs)
> +{
> +	int i;
> +	u64 mask = 0;
> +	union acpi_object *obj;
> +
> +	if (funcs == 0)
> +		return false;
> +
> +	obj = acpi_evaluate_wbrf(handle, rev, 0);
> +	if (!obj)
> +		return false;
> +
> +	if (obj->type != ACPI_TYPE_BUFFER)
> +		return false;
> +
> +	/*
> +	 * Bit vector providing supported functions information.
> +	 * Each bit marks support for one specific function of the WBRF method.
> +	 */
> +	for (i = 0; i < obj->buffer.length && i < 8; i++)
> +		mask |= (u64)obj->buffer.pointer[i] << i * 8;
> +
> +	ACPI_FREE(obj);
> +
> +	if ((mask & BIT(WBRF_ENABLED)) && (mask & funcs) == funcs)
> +		return true;
> +
> +	return false;
> +}

This looks exactly like acpi_check_dsm().

> +
> +/**
> + * 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 = ACPI_COMPANION(dev);
> +
> +	if (!adev)
> +		return false;
> +
> +	if (!acpi_amd_wbrf_supported_system())
> +		return false;
> +
> +	return check_acpi_wbrf(adev->handle,
> +			       WBRF_REVISION,
> +			       BIT(WBRF_RETRIEVE));
> +}
> +EXPORT_SYMBOL_GPL(acpi_amd_wbrf_supported_consumer);

So I would expect this to just use acpi_check_dsm like
is done for the producers.

> +
> +/**
> + * 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.
> + */
> +int amd_wbrf_retrieve_freq_band(struct device *dev,
> +				      struct wbrf_ranges_in_out *out)
> +{
> +	struct acpi_device *adev = ACPI_COMPANION(dev);
> +	struct amd_wbrf_ranges_out acpi_out = {0};
> +	union acpi_object *obj;
> +	int ret = 0;
> +
> +	if (!adev)
> +		return -ENODEV;
> +
> +	obj = acpi_evaluate_wbrf(adev->handle,
> +				 WBRF_REVISION,
> +				 WBRF_RETRIEVE);
> +	if (!obj)
> +		return -EINVAL;

And I would expect this to use acpi_evaluate_dsm(), or
preferably if possible acpi_evaluate_dsm_typed().

Is there any reason why the code is directly calling
a method called WBRF here instead of going through
the _DSM method ?

And if there is such a reason then please update
the documentation to say so, instead of having
the docs clam that consumers also use the _DSM method.

Regards,

Hans