Hi Alan, On Wed, Jul 08, 2015 at 10:43:48AM -0400, Alan Stern wrote:
On Wed, 8 Jul 2015, Rui Miguel Silva wrote:>> --- a/drivers/usb/gadget/udc/dummy_hcd.c >> +++ b/drivers/usb/gadget/udc/dummy_hcd.c >> @@ -1367,8 +1367,10 @@ top: >> /* many requests terminate without a short packet */ >> } else { >> if (req->req.length == req->req.actual >> - && !req->req.zero) >> + && !req->req.zero) { >> req->req.status = 0; >> + *status = 0; >> + } >> if (urb->transfer_buffer_length == urb->actual_length >> && !(urb->transfer_flags >> & URB_ZERO_PACKET)) > >This patch is wrong. *status should indeed remain -EINPROGRESS and the >transfer should remain incomplete. > >Here's an example to illustrate what I mean. Let's say the endpoint's >maxpacket value is 512, and suppose the host queues a 1024-byte IN URB. >In response, suppose the gadget queues two 512-byte requests, each with >req->req.zero clear. Consider what happens when the first request is >processed. > >len, req->req.length and req->req.actual are all equal to 512, and >is_short is false. req therefore completes with req->req.status set to >0. But the URB is still in progress! It still has 512 bytes left to >transfer, and it won't complete until the second request finishes. >Therefore *status (which is the URB's status) should remain set to >-EINPROGRESS. Yes, in this case the patch breaks the flow and remove the URB status of -EINPROGRESS to soon. But what about, and taken your example above, the gadget queues only one 512-byte request? is_short is false, and urb->transfer_buffer_length != urb->actual_length and so the URB status is never changed.Yes, the status never changes. And in fact, that is exactly what would happen if you used a real UDC and a separate host computer instead of dummy-hcd -- the URB would not complete. (In practice the URB would eventually time out or be unlinked for some other reason.)
Understood.
Since we want dummy-hcd to behave as much as possible like a real UDC, we should keep the current code.
Make sense. Thank for the info. Cheers, Rui
Alan Stern
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