On Tuesday 02 May 2017 15:07:03 Laurent Pinchart wrote:
> Hello,
>
> I ran into an issue with a Xilinx Zynq XC7Z010 system. The system acts as a
> USB peripheral, using the UVC gadget driver.
>
> When transferring high bandwidth data over USB in isochronous mode, complete
> system freezes are occasionally noticed. The problem was traced to the
> following code from _hardware_enqueue() in drivers/usb/chipidea/udc.c.
>
> wmb();
> if (hw_read(ci, OP_ENDPTPRIME, BIT(n)))
> goto done;
> do {
> hw_write(ci, OP_USBCMD, USBCMD_ATDTW, USBCMD_ATDTW);
> tmp_stat = hw_read(ci, OP_ENDPTSTAT, BIT(n));
> } while (!hw_read(ci, OP_USBCMD, USBCMD_ATDTW));
> hw_write(ci, OP_USBCMD, USBCMD_ATDTW, 0);
> if (tmp_stat)
> goto done;
>
>
> The do ... while loop loops forever, and as the function is called under a
> spin_lock_irqsave(), the system doesn't appreciate. Adding a maximum number
> of iterations to exit the loop is easy (I'll try to submit a patch after
> finding the root cause of the problem). That fixes the system hang, but USB
> transfers are still broken.
>
> I've checked the code and unfortunately it seems to match the procedure
> documented in the datasheet :-/
>
> The MTBF is several hours, but running 'memtester -M100'
Quick update, this should have read 'memtester 100M', sorry.
> (http://pyropus.ca/software/memtester/) in parallel to UVC video transfer
> over USB brings the MTBF to a few minutes. The problem thus seems to be
> related to memory bus pressure.
>
> Has anyone run into this problem before ? Is this a known issue ? I don't
> mind getting my hands dirty debugging, but as I'm not familiar with the
> chipidea USB controller pointers to what I should check in priority would
> be appreciated.
--
Regards,
Laurent Pinchart
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