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

[Armin Wolf]

Am 27.04.23 um 11:43 schrieb Hans de Goede:

> 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@xxxxxx>
> > ---
> >   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
I like this idea. Returning a negative errno on error would allow drivers to
distinguish between "WMI object not found" and "zero instances found", which
might be useful for some drivers.

Maybe a function for converting ACPI errors to POSIX errors already exists,
otherwise i will just write one myself.

Armin Wolf

> > +
> > +/**
> > + * 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