[1/3] usb: gadget: f_fs: Only return delayed status when len is 0

[Jerry Zhang <zhangjerry@google.com>]

Hi Felipe,

I noticed this wasn't queued up for 4.18. Do you think there is
anything I need to do to get this patch set into 4.19? Also, can we at
least add just this patch ('usb: gadget: f_fs: Only return delayed
status when len is 0') to 4.18 as functionfs control requests won't
work without it?

Thanks,

Jerry
On Mon, Apr 16, 2018 at 6:18 PM Jerry Zhang <zhangjerry@google.com> wrote:
>
> Commit 1b9ba000 ("Allow function drivers to pause control
> transfers") states that USB_GADGET_DELAYED_STATUS is only
> supported if data phase is 0 bytes.
>
> It seems that when the length is not 0 bytes, there is no
> need to explicitly delay the data stage since the transfer
> is not completed until the user responds. However, when the
> length is 0, there is no data stage and the transfer is
> finished once setup() returns, hence there is a need to
> explicitly delay completion.
>
> This manifests as the following bugs:
>
> Prior to 946ef68ad4e4 ('Let setup() return
> USB_GADGET_DELAYED_STATUS'), when setup is 0 bytes, ffs
> would require user to queue a 0 byte request in order to
> clear setup state. However, that 0 byte request was actually
> not needed and would hang and cause errors in other setup
> requests.
>
> After the above commit, 0 byte setups work since the gadget
> now accepts empty queues to ep0 to clear the delay, but all
> other setups hang.
>
> Fixes: 946ef68ad4e4 ("Let setup() return USB_GADGET_DELAYED_STATUS")
> Signed-off-by: Jerry Zhang <zhangjerry@google.com>
> ---
>  drivers/usb/gadget/function/f_fs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index 7d5b1c448eb2..4b2cb9d93176 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -3271,7 +3271,7 @@ static int ffs_func_setup(struct usb_function *f,
>         __ffs_event_add(ffs, FUNCTIONFS_SETUP);
>         spin_unlock_irqrestore(&ffs->ev.waitq.lock, flags);
>
> -       return USB_GADGET_DELAYED_STATUS;
> +       return creq->wLength == 0 ? USB_GADGET_DELAYED_STATUS : 0;
>  }
>
>  static bool ffs_func_req_match(struct usb_function *f,
> --
> 2.17.0.484.g0c8726318c-goog
>
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