[PATCH v2 4/4] usb: gadget: dfu: Fix DFU mode interface descriptor

[Jules Maselbas <jmaselbas@kalray.eu>]

The gadget driver set the bInterfaceProtocol value to 1 in the DFU
interface descriptor. However this value is used to indicate that the
gadget is in run-time mode and not ready for DFU. When ready for DFU
operation the bInterfaceProtocol value must be set to 2 (DFU mode).

From the DFU 1.1 specification, the value of bInterfaceProtocol select:
 - 1: Runtime protocol  (see Table 4.1)
 - 2: DFU mode protocol (see Table 4.4)

This patch change the bInterfaceProtocol value from 1 to 2. As this
DFU gadget driver is always ready for DFU operation (DFU mode) and
doesn't require a USB reset.

Signed-off-by: Jules Maselbas <jmaselbas@kalray.eu>

---

I was getting errors when trying to update a partition using
dfu-util when there was more than one partition available.
(the error was "More than one DFU capable USB device found!")

This is the output of dfu-util when listing partitions.
The first is before this patch and second one is after.
Notice the difference between the two: in the first you
can read 'Found Runtime' where in the other 'Found DFU'.

The bInterfaceProtocol was set to 1 (before):

  $ dfu-util -l
  Found Runtime: [1d6b:0104] [...] alt=0, name="/dev/mtd0.p0"
  Found Runtime: [1d6b:0104] [...] alt=1, name="/dev/mtd0.p1"
  ...

When bInterfaceProtocol is set to 2 (after patch):

  $ dfu-util -l
  Found DFU: [1d6b:0104] [...] alt=0, name="/dev/mtd0.p0"
  Found DFU: [1d6b:0104] [...] alt=1, name="/dev/mtd0.p1"
  ...

---
 drivers/usb/gadget/dfu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/dfu.c b/drivers/usb/gadget/dfu.c
index 225c6e3c6..9117a5b06 100644
--- a/drivers/usb/gadget/dfu.c
+++ b/drivers/usb/gadget/dfu.c
@@ -239,7 +239,7 @@ dfu_bind(struct usb_configuration *c, struct usb_function *f)
 		desc[i].bNumEndpoints	=	0;
 		desc[i].bInterfaceClass =	0xfe;
 		desc[i].bInterfaceSubClass =	1;
-		desc[i].bInterfaceProtocol =	1;
+		desc[i].bInterfaceProtocol =	2;
 		desc[i].bAlternateSetting = i;
 		desc[i].iInterface = us[i + 1].id;
 		header[i] = (struct usb_descriptor_header *)&desc[i];
-- 
2.21.0.196.g041f5ea


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