Re: [PATCH] usb-musb: keep VBUS on when device is disconnected

Bin Liu
2017-03-27T17:17:33Z

On Mon, Mar 27, 2017 at 09:59:47AM -0700, Tony Lindgren wrote:
> * Moreno Bartalucci <moreno.bartalucci@tecnorama.it> [170327 09:23]:
> > If I understood your patch, however, if the device (anyone, not just my one) takes longer to switch, VBUS is deasserted anyway.
>
> Yeah some of them can take at least 10 seconds even to enumerate.
> So probably we need to have to have some longer timeout set for
> OTG_STATE_A_WAIT_BCON, like 20 or 30 seconds.
>
> > Although this patch is working for me, personally I would prefer a solution which would not deassert VBUS. At least on a host only port. Honestly I don’t know how a dual role port should work.
>
> It's been really long time since I read the OTG spec. There
> may be some diagram showing the required timeouts in the spec
> if there is one for VBUS.
>
> Maybe we need some property to specify vbus-always-on-in-host-mode?

The MUSB otg state machine has been changed in many place since the last
time I looked at it, and I am not sure how exactly it works now.

If the $subject patch can correctly keep the VBUS on for host-only mode,
we can somehow use dr_modei value to distinguish the mode. We don't have
to create a new vbus-always-on-in-host-mode flag. VBUS has to be always
on in host-only mode anyway, until some error condition happens.

Regards,
-Bin.