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Subject[PATCH v4 4/6] usb: gadget: add mechanism to specify an explicit status stage
A usb gadget function driver may or may not want to delay the status
stage of a control OUT request. An instance where it might want to is to
asynchronously validate the data of a class-specific request.

A function driver that wants an explicit status stage should set the
newly added explicit_status flag of the usb_request corresponding to the
data stage. Later on the function driver can explicitly complete the
status stage by enqueueing a usb_request for ACK, or calling
usb_ep_set_halt() for STALL.

To support both explicit and implicit status stages, a UDC driver must
call the newly added usb_gadget_control_complete function right after
calling usb_gadget_giveback_request. The status of the request that was
just given back must be fed into usb_gadget_control_complete. To support
the explicit status stage, it might then check what stage the
usb_request was queued in, and for control IN ACK the host's zero-length
data packet, or for control OUT send a zero-length DATA1 ACK packet.

Signed-off-by: Paul Elder <>
Acked-by: Alan Stern <>
v1 Reviewed-by: Laurent Pinchart <>
Changes from v3:

- More specific in commit message about what to do for udc driver acking
- Set explicit_status in usb_gadget_control_complete
- Make explicit_status type bool

Changes from v2:

Add status parameter to usb_gadget_control_complete, so that a
usb_request is not queued if the status of the just given back request
is nonzero.

Changes from v1:

Complete change of API. Now we use a flag that should be set in the
usb_request that is queued for the data stage to signal to the UDC that
we want to delay the status stage (as opposed to setting a flag in the
UDC itself, that persists across all requests). We now also provide a
function for UDC drivers to very easily allow implicit status stages, to
mitigate the need to convert all function drivers to this new API at
once, and to make it easier for UDC drivers to convert.

drivers/usb/gadget/udc/core.c | 34 ++++++++++++++++++++++++++++++++++
include/linux/usb/gadget.h | 10 ++++++++++
2 files changed, 44 insertions(+)

diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
index af88b48c1cea..d3071de2b527 100644
--- a/drivers/usb/gadget/udc/core.c
+++ b/drivers/usb/gadget/udc/core.c
@@ -894,6 +894,40 @@ EXPORT_SYMBOL_GPL(usb_gadget_giveback_request);

/* ------------------------------------------------------------------------- */

+ * usb_gadget_control_complete - complete the status stage of a control
+ * request, or delay it
+ * Context: in_interrupt()
+ *
+ * @gadget: gadget whose control request's status stage should be completed
+ * @explicit_status: true to delay status stage, false to complete here
+ * @status: completion code of previously completed request
+ *
+ * This is called by device controller drivers after returning the completed
+ * request back to the gadget layer, to either complete or delay the status
+ * stage.
+ */
+void usb_gadget_control_complete(struct usb_gadget *gadget,
+ bool explicit_status, int status)
+ struct usb_request *req;
+ if (explicit_status || status)
+ return;
+ /* Send an implicit status-stage request for ep0 */
+ req = usb_ep_alloc_request(gadget->ep0, GFP_ATOMIC);
+ if (req) {
+ req->length = 0;
+ req->explicit_status = 1;
+ req->complete = usb_ep_free_request;
+ usb_ep_queue(gadget->ep0, req, GFP_ATOMIC);
+ }
+/* ------------------------------------------------------------------------- */
* gadget_find_ep_by_name - returns ep whose name is the same as sting passed
* in second parameter or NULL if searched endpoint not found
diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index e5cd84a0f84a..498e3eaa72f1 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -73,6 +73,7 @@ struct usb_ep;
* Note that for writes (IN transfers) some data bytes may still
* reside in a device-side FIFO when the request is reported as
* complete.
+ * @explicit_status: If true, delays the status stage
* These are allocated/freed through the endpoint they're used with. The
* hardware's driver can add extra per-request data to the memory it returns,
@@ -114,6 +115,8 @@ struct usb_request {

int status;
unsigned actual;
+ bool explicit_status;

@@ -850,6 +853,13 @@ extern void usb_gadget_giveback_request(struct usb_ep *ep,


+/* utility to complete or delay status stage */
+void usb_gadget_control_complete(struct usb_gadget *gadget,
+ bool explicit_status, int status);
/* utility to find endpoint by name */

extern struct usb_ep *gadget_find_ep_by_name(struct usb_gadget *g,
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