ehci-hcd.c: fix hanging under higher load

This patch solves a problem with USB hanging under higher load on a
i.MX31 board.  It falls into class of typical USB problems and fixes:
if you don't understand the real cause, add a delay somewhere.

The problem appeared after introduction of ELF relocation, which
results in smaller code, which appears to run faster (probably because
it fits better in the cache); turning off the instruction cache,
adding debug printf()s and increasing the delay have all been found to
make the problem go away.

Moving the original "udelay(1)" up in the code to it's new place made
the problem appear much less frequently. Increasing the delay to 2
microseconds then made the code run reliably in all (hour-long) tests.
To be on the safe side, we set it to 5 microseconds here.

Signed-off-by: Heiko schocher <hs@denx.de>
Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Remy Bohmer <linux@bohmer.net>
Cc: Stefano Babic <sbabic@denx.de>

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index f44fc4e3c4b693117979078adf55d692d83002be..982f96e8b8ff242d7617389f5181abab4238b3fe 100644 (file)
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -205,12 +205,12 @@ static int handshake(uint32_t *ptr, uint32_t mask, uint32_t done, int usec)
        uint32_t result;
        do {
                result = ehci_readl(ptr);
+               udelay(5);
                if (result == ~(uint32_t)0)
                        return -1;
                result &= mask;
                if (result == done)
                        return 0;
-               udelay(1);
                usec--;
        } while (usec > 0);
        return -1;