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

[Kuo-Jung Su]

2013/12/18 Marek Vasut <marex at denx.de>:
> On Wednesday, December 18, 2013 at 08:24:49 AM, Kuo-Jung Su wrote:
>> From: Kuo-Jung Su <dantesu at 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 at faraday-tech.com>
>> CC: Marek Vasut <marex at 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.

>>                       writel(DMAFIFO_CX, &regs->dma_fifo);
>>               } else {
>>                       /* Wait until epx fifo empty */
>
> Best regards,
> Marek Vasut



-- 
Best wishes,
Kuo-Jung Su