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

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.

Fixes: dd4dff8b035f ("USB: composite: Fix bug: should test set_alt function pointer before use it")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 41ab61f9b6e0..002822d98fda 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -1694,9 +1694,7 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
                 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 *gadget, const struct usb_ctrlrequest *ctrl)
                 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) {