[U-Boot] [PATCH 2/2] usb: gadget: fotg210: EP0 fifo empty indication is non-reliable

[Marek Vasut <marex@denx.de>]

On Thursday, December 19, 2013 at 01:50:55 AM, Kuo-Jung Su wrote:
> 2013/12/18 Marek Vasut <marex@denx.de>:
> > On Wednesday, December 18, 2013 at 08:24:49 AM, Kuo-Jung Su wrote:
> >> From: Kuo-Jung Su <dantesu@faraday-tech.com>
> >> 
> >> Because the EP0 fifo empty indication is non-reliable,
> >> an extra delay is necessary to avoid data corruption while
> >> handling packets with size greater than 64 bytes.
> >> 
> >> This workaround should be applied to all hardware revisions.
> >> 
> >> Signed-off-by: Kuo-Jung Su <dantesu@faraday-tech.com>
> >> CC: Marek Vasut <marex@denx.de>
> >> ---
> >> 
> >>  drivers/usb/gadget/fotg210.c |    1 +
> >>  1 file changed, 1 insertion(+)
> >> 
> >> diff --git a/drivers/usb/gadget/fotg210.c b/drivers/usb/gadget/fotg210.c
> >> index e3a61cc..14bfec6 100644
> >> --- a/drivers/usb/gadget/fotg210.c
> >> +++ b/drivers/usb/gadget/fotg210.c
> >> @@ -245,6 +245,7 @@ static int fotg210_dma(struct fotg210_ep *ep, struct
> >> fotg210_request *req) if (ep->id == 0) {
> >> 
> >>                       /* Wait until cx/ep0 fifo empty */
> >>                       fotg210_cxwait(chip, CXFIFO_CXFIFOE);
> >> 
> >> +                     udelay_masked(1);
> > 
> > Why don't you use regular udelay() here please ? Also, how exactly does
> > the delay help solving the unreliability problem please?
> 
> 1. No specific reason at all, I'll use regular udelay() in next version. :)
> 
> 2. The fifo size of ep0 is 64 bytes, and my driver is supposed to make
> sure the fifo empty
>     before filling up the fifo. However there is a hardware bug that
> the fifo empty indication is somehow
>     a bit earlier than fifo reset. So if I don't add an extra delay
> here, the data might be corrupted (i.e., 1 byte missing.)
>     And after a couple of tests, it looks like that 1 usec is good
> enough for this.

Ick, but I guess you guys know the IP blocks' sourcecode.

Best regards,
Marek Vasut