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Subject: Re: [PATCH 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: <20230430203153.5587-1-W_Armin@gmx.de>
 <20230430203153.5587-2-W_Armin@gmx.de>
 <756215f5-d99c-b172-13f6-1a15e026bf65@redhat.com>
From:   Armin Wolf <W_Armin@gmx.de>
Message-ID: <3bfa4a8c-1260-3fc0-9f83-2958467ca596@gmx.de>
Date:   Sun, 30 Apr 2023 23:01:41 +0200
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Precedence: bulk

Am 30.04.23 um 22:41 schrieb Hans de Goede:

> Hi Armin,
>
> On 4/30/23 22:31, 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>
> Thank you for your work on this.
>
>> ---
>>   drivers/platform/x86/wmi.c | 41 ++++++++++++++++++++++++++++++++++++++
>>   include/linux/acpi.h       |  2 ++
>>   include/linux/wmi.h        |  2 ++
>>   3 files changed, 45 insertions(+)
>>
>> diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
>> index c226dd4163a1..5b95d7aa5c2f 100644
>> --- a/drivers/platform/x86/wmi.c
>> +++ b/drivers/platform/x86/wmi.c
>> @@ -263,6 +263,47 @@ 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
>> + *
>> + * Get the number of WMI object instances.
>> + *
>> + * Returns: Number of WMI object instances or negative error code.
>> + */
>> +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)) {
>> +		if (status == AE_BAD_PARAMETER)
>> +			return -EINVAL;
>> +
>> +		return -ENODEV;
> Maybe just return 0 here ?
>
> The GUID not existing at all does not seem like
> an error to me, but rather a case of there
> being 0 instances.
>
> This will also allow patch 2/2 to completely
> drop the get_instance_count() function and
> replace its callers with direct calls to
> wmi_instance_count() as the code is known
> to always pass a valid GUID, so it won't hit
> the -EINVAL path.
>
> Regards,
>
> Hans
>
Hi,

i would prefer returning -ENODEV instead of 0, so WMI drivers can
distinguish between "not found" and "zero instances". Also i do not
think that relying on the parameter of get_instance_count() always
being a valid GUID is a good idea, just in case wmi_instance_count()
is later modified to be able to encounter runtime errors.

Armin Wolf

>
>> +	}
>> +
>> +	return wmidev_instance_count(&wblock->dev);
>> +}
>> +EXPORT_SYMBOL_GPL(wmi_instance_count);
>> +
>> +/**
>> + * 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..e52bf2742eaf 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);
>>
>> +int wmi_instance_count(const char *guid);
>> +
>>   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
>>