linux-kernel - Re: [PATCH] usb: musb: core: Disable the Interrupts till BABBLE is fully handled

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Date:	Mon, 24 Nov 2014 19:09:39 -0600
From:	Felipe Balbi <balbi@...com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	Felipe Balbi <balbi@...com>,
	George Cherian <george.cherian@...com>,
	<gregkh@...uxfoundation.org>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: musb: core: Disable the Interrupts till BABBLE is
 fully handled

On Mon, Nov 24, 2014 at 09:56:28PM +0100, Sebastian Andrzej Siewior wrote:
> On 11/24/2014 09:39 PM, Peter Stuge wrote:
> > Felipe Balbi wrote:
> >>>> A babble only occurs when
> >>>> the device side tries to move data without the host asking for anything.
> >>>
> >>> It also occurs if the device moves more than packet_size bytes. Not
> >>> really helping, I know…
> >>
> >> hmm, why would the device move more than wMaxPacketSize at a time ?
> > 
> > Some devices are buggy.
> 
> for instance if the device comes out of resume and the clock is not yet
> stable but the device sends data. That is not the case here, but an
> example :)

that would be a bug on clk driver, it shouldn't return control to the
user until clk *is* stable :-)

> I *think* for some reason the host did not really receive ep0
> set_config request as planned. And device's answer is probably then
> interpreted as data which is not expected (as Felipe said "device side
> tries to move data without the host asking for anything").

that's definitely a bug, unfortunately I can't think of any Erratum
right now.

> >> That's certainly babble :-)
> > 
> > Certainly! But musb shouldn't fall over or lock up because of it,
> > should it?
> 
> No and the patch fixes the issue. The strange thing is that it only
> happens on the same device. Not if you connect host<->device with two
> boards.

probably some crap going on within the interconnect when both instances
are used.

-- 
balbi

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