Hi, On Mon, Apr 21, 2014 at 10:09 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 21 Apr 2014, Felipe Balbi wrote: > >> Hi, >> >> On Fri, Apr 18, 2014 at 07:34:08PM +0530, sundeep subbaraya wrote: >> >> <snip> >> >> > >> in ep_queue driver starts dma transfer from/to IP buffer to/from req->buf. >> > >> If transfer is completed then request is not added to ep request queue >> > >> and returns from ep_queue. >> > >> If transfer is not completed (actual < length) then request is added >> > >> to queue and returns from ep_queue. >> > > >> > > This is wrong. Why wouldn't you give gadget driver the chance to decide >> > > if it needs to queue the request again or not ? >> > >> > When does gadget driver decides to queue the same request again? >> > if -EBUSY is returned from ep_queue or req.status != 0 in completion >> > routine? >> >> whenever it so decides. Different gadget drivers might have different >> requirements. The code is open and sits under drivers/usb/gadget/ why >> don't you have a read ? > > I get the impression that the two of you are arguing past each other. > It appears that Sundeep is talking about transferring data from the > gadget driver's buffer to an internal buffer in the UDC hardware, but > Felipe is talking about transferring data from the UDC to the host. > > As I understand it, Sundeep said that when the gadget driver queues a > data-IN request, the UDC driver copies as much of the data buffer as > possible into a hardware FIFO. If it succeeds in copying all the data > into the FIFO then the request's completion routine gets called > immediately, even though the data doesn't get sent from the FIFO to the > host until the host asks for it. > > If only part of the data can be copied into the FIFO then the request > is added to the ep's request queue before the usb_ep_queue() call > returns. When space becomes available in the FIFO, the data will be > copied and eventually sent to the host. When all the data has been > copied to the FIFO, the request's completion routine will be called. > > Thus there never is any need for the gadget driver to queue the request > again. An incomplete transfer means the FIFO didn't have enough room > when the request was submitted; it doesn't mean that the data didn't > eventually get sent to the host. Exactly Alan,this is what I was trying to say. Probably I was not clear in explaining. I didnt see any harm this way and even this implementation is same like at91_udc.c. I have been reading mas_storage to understand when does gadget driver tries to enqueue a request again. Since different gadget drivers might have different requirements (agree with Felipe), wanted to know criteria for queuing a same request again. I will change this implementation as per Felipe comments and test with some of the gadgets. Thanks Alan and Felipe, Sundeep > > HTH, > > Alan Stern > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
