linux-kernel - Re: [RFC v2 1/2] platform/x86: wmi: Allow retrieving the number of WMI object instances

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Message-ID: <339c6ba5-6d60-8271-1b5d-6c4165801187@redhat.com>
Date:   Thu, 27 Apr 2023 11:43:49 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Armin Wolf <W_Armin@....de>, markgross@...nel.org
Cc:     Mario.Limonciello@....com, prasanth.ksr@...l.com,
        jorgealtxwork@...il.com, james@...iv.tech,
        Dell.Client.Kernel@...l.com, platform-driver-x86@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 1/2] platform/x86: wmi: Allow retrieving the number of
 WMI object instances

Hi Armin,

Thank you for your work on this.

On 4/26/23 23:28, Armin Wolf wrote:
> Currently, the WMI driver core knows how many instances of a given
> WMI object exist, but WMI drivers cannot access this information.
> At the same time, some current and upcoming WMI drivers want to
> have access to this information. Add wmi_instance_count() and
> wmidev_instance_count() to allow WMI drivers to get the number of
> WMI object instances.
> 
> Signed-off-by: Armin Wolf <W_Armin@....de>
> ---
>  drivers/platform/x86/wmi.c | 40 ++++++++++++++++++++++++++++++++++++++
>  include/linux/acpi.h       |  2 ++
>  include/linux/wmi.h        |  2 ++
>  3 files changed, 44 insertions(+)
> 
> diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
> index c226dd4163a1..7c1a904dec5f 100644
> --- a/drivers/platform/x86/wmi.c
> +++ b/drivers/platform/x86/wmi.c
> @@ -263,6 +263,46 @@ int set_required_buffer_size(struct wmi_device *wdev, u64 length)
>  }
>  EXPORT_SYMBOL_GPL(set_required_buffer_size);
> 
> +/**
> + * wmi_instance_count - Get number of WMI object instances
> + * @guid_string: 36 char string of the form fa50ff2b-f2e8-45de-83fa-65417f2f49ba
> + * @instance_count: variable to hold the instance count
> + *
> + * Get the number of WMI object instances.
> + *
> + * Returns: acpi_status signaling success or error.
> + */
> +acpi_status wmi_instance_count(const char *guid_string, u8 *instance_count)
> +{
> +	struct wmi_block *wblock;
> +	acpi_status status;
> +
> +	status = find_guid(guid_string, &wblock);
> +	if (ACPI_FAILURE(status))
> +		return status;
> +
> +	*instance_count = wmidev_instance_count(&wblock->dev);
> +
> +	return AE_OK;
> +}
> +EXPORT_SYMBOL_GPL(wmi_instance_count);

I would prefer this to have a normal kernel function prototype
which returns -errno rather then returning an acpi_status. E.g. :

/**
 * wmi_instance_count - Get number of WMI object instances
 * @guid_string: 36 char string of the form fa50ff2b-f2e8-45de-83fa-65417f2f49ba
 *
 * Get the number of WMI object instances.
 *
 * Returns: The number of WMI object instances, 0 if the GUID is not found.
 */
int wmi_instance_count(const char *guid_string)
{
	struct wmi_block *wblock;
	acpi_status status;

	status = find_guid(guid_string, &wblock);
	if (ACPI_FAILURE(status))
		return 0;

	return wmidev_instance_count(&wblock->dev);
}
EXPORT_SYMBOL_GPL(wmi_instance_count);

This will also allow this to completely replace
the get_instance_count() function in dell-wmi-sysman.

Note I have just gone with always returning 0 here
on error. I guess you could look at the status and
return 0 for not-found and -errno for other errors
but I don't think any callers will care for the difference,
so just always returning 0 seems easier for callers to
deal with.

As always this is just a suggestion, let me know if
you think this is a bad idea.

Regards,

Hans










> +
> +/**
> + * wmidev_instance_count - Get number of WMI object instances
> + * @wdev: A wmi bus device from a driver
> + *
> + * Get the number of WMI object instances.
> + *
> + * Returns: Number of WMI object instances.
> + */
> +u8 wmidev_instance_count(struct wmi_device *wdev)
> +{
> +	struct wmi_block *wblock = container_of(wdev, struct wmi_block, dev);
> +
> +	return wblock->gblock.instance_count;
> +}
> +EXPORT_SYMBOL_GPL(wmidev_instance_count);
> +
>  /**
>   * wmi_evaluate_method - Evaluate a WMI method (deprecated)
>   * @guid_string: 36 char string of the form fa50ff2b-f2e8-45de-83fa-65417f2f49ba
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index efff750f326d..ab2a4b23e7a3 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -412,6 +412,8 @@ extern bool acpi_is_pnp_device(struct acpi_device *);
> 
>  typedef void (*wmi_notify_handler) (u32 value, void *context);
> 
> +acpi_status wmi_instance_count(const char *guid, u8 *instance_count);
> +
>  extern acpi_status wmi_evaluate_method(const char *guid, u8 instance,
>  					u32 method_id,
>  					const struct acpi_buffer *in,
> diff --git a/include/linux/wmi.h b/include/linux/wmi.h
> index c1a3bd4e4838..763bd382cf2d 100644
> --- a/include/linux/wmi.h
> +++ b/include/linux/wmi.h
> @@ -35,6 +35,8 @@ extern acpi_status wmidev_evaluate_method(struct wmi_device *wdev,
>  extern union acpi_object *wmidev_block_query(struct wmi_device *wdev,
>  					     u8 instance);
> 
> +u8 wmidev_instance_count(struct wmi_device *wdev);
> +
>  extern int set_required_buffer_size(struct wmi_device *wdev, u64 length);
> 
>  /**
> --
> 2.30.2
>