[PATCH v2 2/6] HID: core: Add a hid_is_usb_device() helper function

[Hans de Goede <hdegoede@redhat.com>]

Sometimes HID drivers want to know if the hid_device with which they
are dealing is using the usb_hid_driver. For example this is often
done to check if it is safe to cast hid_device->dev.parent to an
usb_interface like this:

struct usb_interface *intf = to_usb_interface(hdev->dev.parent);

If drivers directly call hid_is_using_ll_driver(hdev, &usb_hid_driver))
for this, then this leads to a "missing symbol usb_hid_driver"
compilation error when CONFIG_USB_HID is not enabled. Requiring
the driver to have a depends on USB_HID in their Kconfig entry
to work around this.

Add a hid_is_usb_device() helper function which drivers can use
to safely check if they are dealing with a usb_hid device without
needing to worry about the CONFIG_USB_HID setting.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/hid/hid-core.c | 10 ++++++++++
 include/linux/hid.h    |  1 +
 2 files changed, 11 insertions(+)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index b593dff411a6..294c3cf05d85 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -2590,6 +2590,16 @@ int hid_check_keys_pressed(struct hid_device *hid)
 }
 EXPORT_SYMBOL_GPL(hid_check_keys_pressed);
 
+bool hid_is_usb_device(struct hid_device *hid)
+{
+#if IS_ENABLED(CONFIG_USB_HID)
+	return hid_is_using_ll_driver(hid, &usb_hid_driver);
+#else
+	return false;
+#endif
+}
+EXPORT_SYMBOL_GPL(hid_is_usb_device);
+
 static int __init hid_init(void)
 {
 	int ret;
diff --git a/include/linux/hid.h b/include/linux/hid.h
index ef702b3f56e3..6ceadc234132 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -901,6 +901,7 @@ struct hid_report *hid_validate_values(struct hid_device *hid,
 void hid_setup_resolution_multiplier(struct hid_device *hid);
 int hid_open_report(struct hid_device *device);
 int hid_check_keys_pressed(struct hid_device *hid);
+bool hid_is_usb_device(struct hid_device *hid);
 int hid_connect(struct hid_device *hid, unsigned int connect_mask);
 void hid_disconnect(struct hid_device *hid);
 bool hid_match_one_id(const struct hid_device *hdev,
-- 
2.31.1