[U-Boot] USB Host not enumerating properly on AM335x-based board

[Maxime Ripard <maxime.ripard@free-electrons.com>]

Hi Anatolij,

On Sat, Nov 22, 2014 at 12:40:58AM +0100, Anatolij Gustschin wrote:
> > The same USB port with the same device works fine under Linux.
> > 
> > The VBUS pin is still up after running the command, so it's not really
> > a matter of power being shut down on the bus.
> > 
> > I'm kind of running out of idea on what to test next. The differences
> > between u-boot's musb-new and Linux' own musb driver seems thin and to
> > make sense, so I don't think the driver itself is to blame.
> > 
> > Anyone experienced such a thing?
> 
> We experienced similar thing this week, but on an imx6dl based board.
> Quite a lot of debugging and comparison with USB host operation under
> Linux didn't really help much. Finally we found the issue with the
> timer implementation, udelay(1) took too much time, about 35 usec.
> Whereas one would expect it to take about 1 usec, ideally.
> EHCI-HCD, USB-Hub and Storage drivers in U-Boot use udelay()/mdelay()
> quite extensively. Reworking the timer implementation for our
> platform resulted in udelay(1) times taking about 2.5 usec. This was
> enough for USB driver code to work again.

I just gave it a try.

mdelay(1000) and udelay (1000 * 1000) are both taking around 1s
(1.0002... for udelay, 1.13... for mdelay).

udelay(1) on the other hand takes around 151us, which seems to be the
same overhead we saw for udelay(1000 * 1000).

While that looks really high with regard to what you were saying, but
I just tested it with a beaglebone black that have similar delay
values, and yet the usb storage works as expected. So I don't think
it's really the issue there :/

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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