usb: gadget: fotg210: EP0 fifo empty indication is non-reliable

The fifo size of ep0 is 64 bytes, and if the packet size grater than
64 bytes, the driver would have to fill up the fifo multiple times,
and before filling up the fifo, the driver should make sure the fifo
is empty by checking fifo empty indication.

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)

After a couple of tests, it truns out that 1 usec is good enough.

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>

diff --git a/drivers/usb/gadget/fotg210.c b/drivers/usb/gadget/fotg210.c
index cc5c507f875e0e5ccb44a826d4ecfe5acdd48d86..3acf6a1f41dfd35897d84262871c71f5203e1de3 100644 (file)
--- 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(1);
                        writel(DMAFIFO_CX, &regs->dma_fifo);
                } else {
                        /* Wait until epx fifo empty */