usb: gadgetfs: return USB_GADGET_DELAYED_STATUS from setup()

Return USB_GADGET_DELAYED_STATUS from the setup() callback for 0-length
transfers as a workaround to stop some UDC drivers (e.g. dwc3) from
automatically proceeding with the status stage.

This workaround should be removed once all UDC drivers are fixed to
always delay the status stage until a response is queued to EP0.

Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://lore.kernel.org/r/a8d2b91f9890dc21daa359183e84879ff4525180.1693237258.git.andreyknvl@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index ce9e31f..6b929de 100644 (file)
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -31,6 +31,12 @@
 
 #include <linux/usb/gadgetfs.h>
 #include <linux/usb/gadget.h>
+#include <linux/usb/composite.h> /* for USB_GADGET_DELAYED_STATUS */
+
+/* Undef helpers from linux/usb/composite.h as gadgetfs redefines them */
+#undef DBG
+#undef ERROR
+#undef INFO
 
 
 /*
@@ -1511,7 +1517,16 @@ delegate:
                        event->u.setup = *ctrl;
                        ep0_readable (dev);
                        spin_unlock (&dev->lock);
-                       return 0;
+                       /*
+                        * Return USB_GADGET_DELAYED_STATUS as a workaround to
+                        * stop some UDC drivers (e.g. dwc3) from automatically
+                        * proceeding with the status stage for 0-length
+                        * transfers.
+                        * Should be removed once all UDC drivers are fixed to
+                        * always delay the status stage until a response is
+                        * queued to EP0.
+                        */
+                       return w_length == 0 ? USB_GADGET_DELAYED_STATUS : 0;
                }
        }