Re: [PATCH v4 5/6] usb: musb: gadget: implement optional explicit status stage

From: Alan Stern
Date: Sun Jan 06 2019 - 15:04:01 EST

On Sun, 6 Jan 2019, Paul Elder wrote:

> Implement the mechanism for optional explicit status stage for the MUSB
> driver. This allows a function driver to specify what to reply for the
> status stage. The functionality for an implicit status stage is
> retained.
> Signed-off-by: Paul Elder <paul.elder@xxxxxxxxxxxxxxxx>
> v1 Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> v1 Acked-by: Bin Liu <b-liu@xxxxxx>
> ---
> No change from v3
> Changes from v2:
> - update call to usb_gadget_control_complete to include status
> - since sending STALL from the function driver is now done with
> usb_ep_set_halt, there is no need for the internal ep0_send_response to
> take a stall/ack parameter; remove the parameter and make the function
> only send ack, and remove checking for the status reply in the
> usb_request for the status stage
> Changes from v1:
> - obvious change to implement v2 mechanism laid out by 4/6 of this
> series (send_response, and musb_g_ep0_send_response function has
> been removed, call to usb_gadget_control_complete has been added)
> - ep0_send_response's ack argument has been changed from stall
> - last_packet flag in ep0_rxstate has been removed, since it is equal to
> req != NULL
> drivers/usb/musb/musb_gadget.c | 2 ++
> drivers/usb/musb/musb_gadget_ep0.c | 23 +++++++++++++++++++++++
> 2 files changed, 25 insertions(+)
> diff --git a/drivers/usb/musb/musb_gadget.c b/drivers/usb/musb/musb_gadget.c
> index d3f33f449445..a7a992ab0c9d 100644
> --- a/drivers/usb/musb/musb_gadget.c
> +++ b/drivers/usb/musb/musb_gadget.c
> @@ -145,6 +145,8 @@ __acquires(ep->musb->lock)
> trace_musb_req_gb(req);
> usb_gadget_giveback_request(&req->ep->end_point, &req->request);
> + usb_gadget_control_complete(&musb->g, request->explicit_status,
> + request->status);

I haven't paid much attention to this part of the patch series, not
knowing much about musb. Still, it's clear that
usb_gadget_control_complete should be called only for transfers on
ep0. You need to test the endpoint value.

Another problem: the completion handler may deallocate the request.
Dereferencing request->expicit_status and request->status would then
cause errors. Would it be preferable to call
usb_gadget_control_complete before usb_gadget_giveback_request? If
it gets done that way then the arguments could be simplified: we could
pass a pointer to the request instead of the separate explicit_status
and status values.

Alan Stern