[PATCH 3/3] usb: gadgetfs: return USB_GADGET_DELAYED_STATUS from setup()

[andrey.konovalov@linux.dev]

From: Andrey Konovalov <andreyknvl@gmail.com>

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.

Signed-off-by: Andrey Konovalov <andreyknvl@gmail.com>
---
 drivers/usb/gadget/legacy/inode.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 28249d0bf062..154bbf578ba2 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -31,6 +31,7 @@
 
 #include <linux/usb/gadgetfs.h>
 #include <linux/usb/gadget.h>
+#include <linux/usb/composite.h>
 
 
 /*
@@ -241,6 +242,7 @@ static DEFINE_MUTEX(sb_mutex);		/* Serialize superblock operations */
 #define xprintk(d,level,fmt,args...) \
 	printk(level "%s: " fmt , shortname , ## args)
 
+#undef DBG
 #ifdef DEBUG
 #define DBG(dev,fmt,args...) \
 	xprintk(dev , KERN_DEBUG , fmt , ## args)
@@ -256,8 +258,10 @@ static DEFINE_MUTEX(sb_mutex);		/* Serialize superblock operations */
 	do { } while (0)
 #endif /* DEBUG */
 
+#undef ERROR
 #define ERROR(dev,fmt,args...) \
 	xprintk(dev , KERN_ERR , fmt , ## args)
+#undef INFO
 #define INFO(dev,fmt,args...) \
 	xprintk(dev , KERN_INFO , fmt , ## args)
 
@@ -1511,7 +1515,16 @@ gadgetfs_setup (struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 			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;
 		}
 	}
 
-- 
2.25.1