usb: gadget: f_fs: add capability for dfu functional descriptor

Add the ability for the USB FunctionFS (FFS) gadget driver to be able
to create Device Firmware Upgrade (DFU) functional descriptors. [1]

This patch allows implementation of DFU in userspace using the
FFS gadget. The DFU protocol uses the control pipe (ep0) for all
messaging so only the addition of the DFU functional descriptor
is needed in the kernel driver.

The DFU functional descriptor is written to the ep0 file along with
any other descriptors during FFS setup. DFU requires an interface
descriptor followed by the DFU functional descriptor.

This patch includes documentation of the added descriptor for DFU
and conversion of some existing documentation to kernel-doc format
so that it can be included in the generated docs.

An implementation of DFU 1.1 that implements just the runtime descriptor
using the FunctionFS gadget (with rebooting into u-boot for DFU mode)
has been tested on an i.MX8 Nano.

An implementation of DFU 1.1 that implements both runtime and DFU mode
using the FunctionFS gadget has been tested on Xilinx Zynq UltraScale+.
Note that for the best performance of firmware update file transfers, the
userspace program should respond as quick as possible to the setup packets.

[1] https://www.usb.org/sites/default/files/DFU_1.1.pdf

Signed-off-by: David Sands <david.sands@biamp.com>
Co-developed-by: Chris Wulff <crwulff@gmail.com>
Signed-off-by: Chris Wulff <crwulff@gmail.com>
Link: https://lore.kernel.org/r/20240811000004.1395888-2-crwulff@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index e0ceaa721949..e35177fc6c55 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -2478,7 +2478,7 @@ typedef int (*ffs_os_desc_callback)(enum ffs_os_desc_type entity,
 
 static int __must_check ffs_do_single_desc(char *data, unsigned len,
 					   ffs_entity_callback entity,
-					   void *priv, int *current_class)
+					   void *priv, int *current_class, int *current_subclass)
 {
 	struct usb_descriptor_header *_ds = (void *)data;
 	u8 length;
@@ -2535,6 +2535,7 @@ static int __must_check ffs_do_single_desc(char *data, unsigned len,
 		if (ds->iInterface)
 			__entity(STRING, ds->iInterface);
 		*current_class = ds->bInterfaceClass;
+		*current_subclass = ds->bInterfaceSubClass;
 	}
 		break;
 
@@ -2559,6 +2560,12 @@ static int __must_check ffs_do_single_desc(char *data, unsigned len,
 			if (length != sizeof(struct ccid_descriptor))
 				goto inv_length;
 			break;
+		} else if (*current_class == USB_CLASS_APP_SPEC &&
+			   *current_subclass == USB_SUBCLASS_DFU) {
+			pr_vdebug("dfu functional descriptor\n");
+			if (length != sizeof(struct usb_dfu_functional_descriptor))
+				goto inv_length;
+			break;
 		} else {
 			pr_vdebug("unknown descriptor: %d for class %d\n",
 			      _ds->bDescriptorType, *current_class);
@@ -2621,6 +2628,7 @@ static int __must_check ffs_do_descs(unsigned count, char *data, unsigned len,
 	const unsigned _len = len;
 	unsigned long num = 0;
 	int current_class = -1;
+	int current_subclass = -1;
 
 	for (;;) {
 		int ret;
@@ -2640,7 +2648,7 @@ static int __must_check ffs_do_descs(unsigned count, char *data, unsigned len,
 			return _len - len;
 
 		ret = ffs_do_single_desc(data, len, entity, priv,
-			&current_class);
+			&current_class, &current_subclass);
 		if (ret < 0) {
 			pr_debug("%s returns %d\n", __func__, ret);
 			return ret;