[PATCH] USB: allow some usb functions to take a const pointer.

[Greg Kroah-Hartman]

The functions to_usb_interface(), to_usb_device, and
interface_to_usbdev() sometimes would like to take a const * and return
a const * back.  As we are doing pointer math, a call to container_of()
loses the const-ness of a pointer, so use a _Generic() macro to pick the
proper inline function to call instead.

Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/usb.h | 55 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 52 insertions(+), 3 deletions(-)

diff --git a/include/linux/usb.h b/include/linux/usb.h
index 9ff1ad4dfad1..3a55131e0ad4 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -258,7 +258,27 @@ struct usb_interface {
 	struct device *usb_dev;
 	struct work_struct reset_ws;	/* for resets in atomic context */
 };
-#define	to_usb_interface(d) container_of(d, struct usb_interface, dev)
+
+static inline struct usb_interface *__to_usb_interface(struct device *d)
+{
+	return container_of(d, struct usb_interface, dev);
+}
+
+static inline const struct usb_interface *__to_usb_interface_const(const struct device *d)
+{
+	return container_of(d, struct usb_interface, dev);
+}
+
+/*
+ * container_of() will happily take a const * and spit back a non-const * as it
+ * is just doing pointer math.  But we want to be a bit more careful in the USB
+ * driver code, so manually force any const * of a device to also be a const *
+ * to a usb_device.
+ */
+#define to_usb_interface(dev)						\
+	_Generic((dev),							\
+		 const struct device *: __to_usb_interface_const,	\
+		 struct device *: __to_usb_interface)(dev)
 
 static inline void *usb_get_intfdata(struct usb_interface *intf)
 {
@@ -709,12 +729,41 @@ struct usb_device {
 	u16 hub_delay;
 	unsigned use_generic_driver:1;
 };
-#define	to_usb_device(d) container_of(d, struct usb_device, dev)
 
-static inline struct usb_device *interface_to_usbdev(struct usb_interface *intf)
+static inline struct usb_device *__to_usb_device(struct device *d)
+{
+	return container_of(d, struct usb_device, dev);
+}
+
+static inline const struct usb_device *__to_usb_device_const(const struct device *d)
+{
+	return container_of(d, struct usb_device, dev);
+}
+
+/*
+ * container_of() will happily take a const * and spit back a non-const * as it
+ * is just doing pointer math.  But we want to be a bit more careful in the USB
+ * driver code, so manually force any const * of a device to also be a const *
+ * to a usb_device.
+ */
+#define to_usb_device(dev)					\
+	_Generic((dev),						\
+		 const struct device *: __to_usb_device_const,	\
+		 struct device *: __to_usb_device)(dev)
+
+static inline struct usb_device *__intf_to_usbdev(struct usb_interface *intf)
 {
 	return to_usb_device(intf->dev.parent);
 }
+static inline const struct usb_device *__intf_to_usbdev_const(const struct usb_interface *intf)
+{
+	return to_usb_device((const struct device *)intf->dev.parent);
+}
+
+#define interface_to_usbdev(intf)					\
+	_Generic((intf),						\
+		 const struct usb_interface *: __intf_to_usbdev_const,	\
+		 struct usb_interface *: __intf_to_usbdev)(intf)
 
 extern struct usb_device *usb_get_dev(struct usb_device *dev);
 extern void usb_put_dev(struct usb_device *dev);
-- 
2.38.0