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

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.

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

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 3a769f2..ad03c6d 100644 (file)
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -1126,9 +1126,7 @@ 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;
@@ -1137,7 +1135,13 @@ 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) {