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

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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




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