[PATCH v2 2/3] usb: core: Allow subclassed USB drivers to override usb_choose_configuration()

[Douglas Anderson]

For some USB devices we might want to do something different for
usb_choose_configuration(). One example here is the r8152 driver where
we want to end up using the vendor driver with the preferred
interface.

The r8152 driver tried to make things work by implementing a USB
generic_subclass driver and then overriding the normal config
selection after it happened. This is less than ideal and also caused
breakage if someone deauthorized and re-authorized the USB device
because the USB core ended up going back to it's default logic for
choosing the best config. I made an attempt to fix this [1] but it was
a bit ugly.

Let's do this better and allow USB generic_subclass drivers to
override usb_choose_configuration().

[1] https://lore.kernel.org/r/20231130154337.1.Ie00e07f07f87149c9ce0b27ae4e26991d307e14b@changeid

Suggested-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---

Changes in v2:
- ("Allow subclassed USB drivers to override ...") new for v2.

 drivers/usb/core/generic.c | 7 +++++++
 include/linux/usb.h        | 6 ++++++
 2 files changed, 13 insertions(+)

diff --git a/drivers/usb/core/generic.c b/drivers/usb/core/generic.c
index 740342a2812a..dcb897158228 100644
--- a/drivers/usb/core/generic.c
+++ b/drivers/usb/core/generic.c
@@ -59,10 +59,17 @@ int usb_choose_configuration(struct usb_device *udev)
 	int num_configs;
 	int insufficient_power = 0;
 	struct usb_host_config *c, *best;
+	struct usb_device_driver *udriver = to_usb_device_driver(udev->dev.driver);
 
 	if (usb_device_is_owned(udev))
 		return 0;
 
+	if (udriver->choose_configuration) {
+		i = udriver->choose_configuration(udev);
+		if (i >= 0)
+			return i;
+	}
+
 	best = NULL;
 	c = udev->config;
 	num_configs = udev->descriptor.bNumConfigurations;
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 8c61643acd49..618e5a0b1a22 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -1264,6 +1264,9 @@ struct usb_driver {
  *	module is being unloaded.
  * @suspend: Called when the device is going to be suspended by the system.
  * @resume: Called when the device is being resumed by the system.
+ * @choose_configuration: If non-NULL, called instead of the default
+ *	usb_choose_configuration(). If this returns an error then we'll go
+ *	on to call the normal usb_choose_configuration().
  * @dev_groups: Attributes attached to the device that will be created once it
  *	is bound to the driver.
  * @drvwrap: Driver-model core structure wrapper.
@@ -1287,6 +1290,9 @@ struct usb_device_driver {
 
 	int (*suspend) (struct usb_device *udev, pm_message_t message);
 	int (*resume) (struct usb_device *udev, pm_message_t message);
+
+	int (*choose_configuration) (struct usb_device *udev);
+
 	const struct attribute_group **dev_groups;
 	struct usbdrv_wrap drvwrap;
 	const struct usb_device_id *id_table;
-- 
2.43.0.rc2.451.g8631bc7472-goog