> -----Original Message----- > From: Alan Stern [mailto:[EMAIL PROTECTED] > Sent: Thursday, July 14, 2005 10:01 PM > To: Li Yang-r58472 > Cc: linux-usb-devel@lists.sourceforge.net > Subject: RE: [linux-usb-devel] question about mass storage gadget > > On Thu, 14 Jul 2005, Li Yang-r58472 wrote: > > > Ok. Let's change the situation to that client reply shorter DATA than > > host CBW requested. There will be a stall and CSW. > > Yes, that happens normally. > > > > > At this time, the bulk-in ep is halted, there is a CSW request queued > in > > > > the bulk-in ep, and clear_feature can't be executed as the queue is not > > > > empty. They form a dead-lock, and stop working. > > > > > > You're a little confused. Above you mentioned that set_halt fails if the > > > queue is non-empty, which is correct. Here you state that clear_halt > > > fails if the queue is non-empty, and that's wrong. > > > > I think it's reasonable to check the queue doing set_halt while ignore > > it when clear_halt. However, looking into set_halt function in omap udc > > driver, it returns -EAGAIN when the queue is not empty for both > > set_halt/clear_halt operations. > > It should have been tested, which makes me really confused. > > You're still mixed up. The gadget driver does call the set_halt function, > but it doesn't call clear_halt. The Clear-Halt message is sent by the > host and handled directly by the controller driver. The gadget driver > isn't involved.
Seems I didn't state the problem clearly. I agree that there is no problem with the mass-storage gadget driver. But the problem becomes how to deal with host's clear_feature request in device controller driver. Do we need to check the queue in udc when doing set_halt() for value equals either 0 or 1 as in omap_udc? > > > > > How did we do to avoid such a situation? Or to break it? > > > > > > You might ask more generally: What happens if the gadget driver tries to > > > halt the bulk-in endpoint when there is data in the queue and the host > > > isn't reading it? Answer: The gadget will hang until the host issues > > > either a class-specific reset or a USB port reset. > > > > Yes, that's the phenomenon I got when the clear_halt hangs. Host keep > > resetting once for a while. > > What clear_halt are you talking about? The only calls to clear_halt in > file_storage.c occur in the handle_exceptions routine, which calls > usb_ep_fifo_flush first. So the queues will be empty when clear_halt is > called. > > Alan Stern ------------------------------------------------------- SF.Net email is sponsored by: Discover Easy Linux Migration Strategies from IBM. Find simple to follow Roadmaps, straightforward articles, informative Webcasts and more! Get everything you need to get up to speed, fast. http://ads.osdn.com/?ad_idt77&alloc_id492&op=click _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
