Re: Changes to power management in ehci-tegra

[Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>]

On 04/17/2012 08:56 AM, Alan Stern wrote:
> On Mon, 16 Apr 2012, Stephen Warren wrote:
> 
>>>> The EHCI controller's active_kids count stays at 1 all the time. I
>>>> assume that's the root USB hub device. Looking in its power/ directory,
>>>> I see that even when nothing is plugged in, runtime_status==enabled,
>>>> even with no active_kids or runtime_usage:
>>>
>>> That does indeed sound like a bug.

Aha, there's a CONFIG_USB_SUSPEND which I didn't have enabled. Now I see
the controller suspending.

However, the controller suspends immediately the system boots even if
there's a device already connected, and never resumes if there wasn't
connected at boot, but one is plugged in later.

In this state, I must set tegra-ehci.2/usb3/power/control=on to get
anything to work. Forcing just the controller on
(tegra-ehci.2/power/control=on) doesn't fix this.

After than, I can set tegra-ehci.2/usb3/power/control=auto, and see the
root hub (tegra-ehci.2/usb3/power) suspending/resuming as devices are
unplugged/plugged.

I just can't have tegra-ehci.2/power/control=auto while nothing is
plugged in, or the cycle starts again.

I assume this a bug in the Tegra EHCI driver's suspend implementation?