[U-Boot] [PATCH] usb: Fix device detection code

[Marek Vasut <marex@denx.de>]

On Wednesday, August 05, 2015 at 03:42:11 PM, Hans de Goede wrote:
> Hi,
> 
> On 05-08-15 03:19, Marek Vasut wrote:
> > The code in question polls an USB port status via USB_REQ_GET_STATUS
> > to determine whether there is a device on the port or not. The way to
> > figure that out is to check two bits. Those are wPortChange[0] and
> > wPortStatus[0].
> > 
> > The wPortChange[0] indicates whether some kind of a connection status
> > change happened on a port (a device was plugged or unplugged). The
> > wPortStatus[0] bit indicates the status of the connection (plugged or
> > unplugged).
> > 
> > The current code tests whether wPortChange[0] == wPortStatus[0] and
> > if that's the case, considers the loop polling for the presence of a
> > USB device on port finished.
> > 
> > This works for most USB sticks, since they come up really quickly and
> > trigger the USB port change detection before the first iteration of the
> > detection loop happens. Thus, both wPortChange[0] and wPortStatus[0]
> > are set to 1 and thus equal. The loop is existed in it's first iteration
> > and the stick is detected correctly.
> > 
> > The problem is with some obscure USB sticks, which take some time before
> > they pop up on the bus after the port was enabled. In this case, both
> > the wPortChange[0] and wPortStatus[0] are 0. They are equal again, so
> > the loop again exits in the first iteration, but this is incorrect, as
> > such USB stick didn't have the opportunity to get detected on the bus.
> > 
> > Rework the code such, that it checks for wPortChange[0] first to test
> > if any connection change happened at all. If no change occured, keep
> > polling. If a change did occur, test the wPortStatus[0] to see there is
> > some device present on the port and only if this is the case, break out
> > of the polling loop.
> > 
> > This patch also trims down the duration of the polling loop from 10s
> > per port to 1s per port. This is still annoyingly long, but there is
> > no better option in case of U-Boot unfortunatelly. This change will
> > most likely increase the duration of 'usb start' on some platforms,
> > but this is needed to fix a bug.
> > 
> > Signed-off-by: Marek Vasut <marex@denx.de>
> > Cc: Simon Glass <sjg@chromium.org>
> > Cc: Hans de Goede <hdegoede@redhat.com>
> 
> Looks good to me:
> 
> Reviewed-by: Hans de Goede <hdegoede@redhat.com>

OK, let's apply it and see if anyone complains :)

Thanks for checking it!