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Subject: Re: [RFC v2 1/2] platform/x86: wmi: Allow retrieving the number of
 WMI object instances
To:     Hans de Goede <hdegoede@redhat.com>, markgross@kernel.org
Cc:     Mario.Limonciello@amd.com, prasanth.ksr@dell.com,
        jorgealtxwork@gmail.com, james@equiv.tech,
        Dell.Client.Kernel@dell.com, platform-driver-x86@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20230426212848.108562-1-W_Armin@gmx.de>
 <20230426212848.108562-2-W_Armin@gmx.de>
 <339c6ba5-6d60-8271-1b5d-6c4165801187@redhat.com>
From:   Armin Wolf <W_Armin@gmx.de>
Message-ID: <4db0e619-7f18-3f6b-9fb3-769f95233a72@gmx.de>
Date:   Thu, 27 Apr 2023 18:26:30 +0200
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Precedence: bulk

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@gmx.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
>
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
>>