Patch "usb: gadget: composite: Test get_alt() presence instead of set_alt()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

usb: gadget: composite: Test get_alt() presence instead of set_alt()

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
usb-gadget-composite-test-get_alt-presence-instead-of-set_alt.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Krzysztof Opasiak <[email protected]>
Date: Tue, 20 Dec 2016 19:52:16 +0100
Subject: usb: gadget: composite: Test get_alt() presence instead of set_alt()

From: Krzysztof Opasiak <[email protected]>

commit 7e4da3fcf7c9fe042f2f7cb7bf23861a899b4a8f upstream.

By convention (according to doc) if function does not provide get_alt() callback composite framework should assume that it has only altsetting 0 and should respond with error if host tries to set other one.

After commit dd4dff8b035f ("USB: composite: Fix bug: should test set_alt function pointer before use it")
we started checking set_alt() callback instead of get_alt(). This check is useless as we check if set_alt() is set inside usb_add_function() and fail if it's NULL.

Let's fix this check and move comment about why we check the get method instead of set a little bit closer to prevent future false fixes.

---
 drivers/usb/gadget/composite.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

@@ -1694,9 +1694,7 @@ composite_setup(struct usb_gadget *gadge
 		value = min(w_length, (u16) 1);
 		break;
 
-	/* function drivers must handle get/set altsetting; if there's
-	 * no get() method, we know only altsetting zero works.
-	 */
+	/* function drivers must handle get/set altsetting */
 	case USB_REQ_SET_INTERFACE:
 		if (ctrl->bRequestType != USB_RECIP_INTERFACE)
 			goto unknown;

@@ -1705,7 +1703,13 @@ composite_setup(struct usb_gadget *gadge
 		f = cdev->config->interface[intf];
 		if (!f)
 			break;
-		if (w_value && !f->set_alt)
+
+		/*
+		 * If there's no get_alt() method, we know only altsetting zero
+		 * works. There is no need to check if set_alt() is not NULL
+		 * as we check this in usb_add_function().
+		 */
+		if (w_value && !f->get_alt)
 			break;
 		value = f->set_alt(f, w_index, w_value);
 		if (value == USB_GADGET_DELAYED_STATUS) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/usb-gadget-composite-test-get_alt-presence-instead-of-set_alt.patch