Hi Julius,
On Thu, May 29, 2014 at 4:07 AM, Julius Werner <[email protected]> wrote:
> We originally tried using this driver on ChromiumOS and never got it
> to work reliably. IIRC the issue was that if the hub had already been
> initialized by firmware, the USB stack might enumerate it before the
> usb3503 driver is probed and then the later reset will silently
> disrupt that connection. (I think I tried to force the 3503 to probe
> earlier as well, and there was some other issue with that although I
> don't recall the details.)
Ok, there was already a patch posted by you for this[1], which had
quite a much discussion
on it.
Would you like to give some pointers based on that ?
One that Olof had suggested was to use gpio-reset driver which is yet
to make to mainline.
But i think with that too we need to take care of the timing for
resetting the hub before PHY
gets reset.
>
> This will not be an issue for the Snow and Peach_Pi(t) boards (since
> neither of them shipped with firmware that supports this hub), but it
> will be an issue for Spring and Skate. On ChromiumOS we decided to
> carry a local (and admittedly ugly) patch to pull that reset line from
> the USB PHY driver instead, since that's the only way I could get it
> to work in all cases (see http://crosreview.com/58963).
>
> This doesn't mean I'm against this patch per se, just wanted to point
> out the trade-offs.
Thanks for raising the concern, this needs to be addressed.
[1] https://lkml.org/lkml/2013/7/9/486
--
Best Regards
Vivek Gautam
Samsung R&D Institute, Bangalore
India
> Ok, there was already a patch posted by you for this[1], which had
> quite a much discussion
> on it.
> Would you like to give some pointers based on that ?
> One that Olof had suggested was to use gpio-reset driver which is yet
> to make to mainline.
> But i think with that too we need to take care of the timing for
> resetting the hub before PHY
> gets reset.
Oh, right, I remember now. Seems like there wasn't much consensus on
how to solve the problem there, and I think I didn't really have time
to work on it any more either.
I think coupling in another driver to reset the device isn't a bad
idea... this could even be usb3503 if you modified it a little, and it
could also address Tomasz' concerns from that thread that the solution
should be extensible to other HSIC devices that need a different reset
sequence. But you need some mechanism to hook the two drivers together
and make sure phy-samsung-usb2 synchronously calls the reset function
at exactly the right point to ensure the timing works right.