linux-kernel - Re: [PATCH] usb: dwc3: gadget: call gadget driver's ->suspend/->resume

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Message-ID: <20150424205625.GA10838@psi-dev26.jf.intel.com>
Date:	Fri, 24 Apr 2015 13:56:25 -0700
From:	David Cohen <david.a.cohen@...ux.intel.com>
To:	Felipe Balbi <balbi@...com>
Cc:	gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] usb: dwc3: gadget: call gadget driver's
 ->suspend/->resume

On Fri, Apr 24, 2015 at 02:48:27PM -0500, Felipe Balbi wrote:
> Hi,

Hi Felipe,

> 
> On Thu, Apr 23, 2015 at 03:37:48PM -0700, David Cohen wrote:
> > On Fri, Apr 17, 2015 at 02:43:27PM -0500, Felipe Balbi wrote:
> > > On Fri, Apr 17, 2015 at 11:41:56AM -0700, David Cohen wrote:
> > > > From: Felipe Balbi <balbi@...com>
> > > 
> > > missing the required:
> > > 
> > > [ Upstream commit bc5ba2e0b829c9397f96df1191c7d2319ebc36d9 ]
> > > 
> > > > 
> > > > When going into bus suspend/resume we _must_
> > > > call gadget driver's ->suspend/->resume callbacks
> > > > accordingly. This patch implements that very feature
> > > > which has been missing forever.
> > > > 
> > > > Cc: <stable@...r.kernel.org> # 3.14
> > > > Signed-off-by: Felipe Balbi <balbi@...com>
> > > > Signed-off-by: David Cohen <david.a.cohen@...ux.intel.com>
> > > > ---
> > > > 
> > > > Hi,
> > > > 
> > > > This patch was introduced on v3.15.
> > > > But the issue it fixes already existed on v3.14 and v3.14 is a long term
> > > > support version.
> > > 
> > > Can you show me a log of this breaking anywhere ? Why do you consider
> > > this a bug fix ? What sort of drawbacks did you notice ?
> > 
> > We're seeing BC1.2 compliance test failure. I borrowed this info from
> > the bug report :)
> > 
> > 1. BC1.2 compliance testing - SDP2.0
> > -----------------------------------------------
> > 1. On Connect to active Host (Expected result: 100mA to 500mA):
> >    Actual result 100mA to 500mA
> > 
> > 2. On Host Suspend (ER: Fall back to 0mA):
> >    not falling back to 0mA, remains at 500mA
> > 
> > 3. On Connect to Suspended Host (ER: 100mA to 0mA):
> >    cable-props shown as 100mA, which means drawing a current of 100mA from
> >    Suspended Host
> > 
> > 4. On making Host active (ER: 500mA):
> >    500mA
> 
> But we don't support Battery Charging with dwc3 as of now :-) In fact,
> just note that none of the BC registers are even defined in the current
> driver anywhere. Seems like you should cherry-pick these to your vendor
> tree, but v3.14 vanilla, because it doesn't support BC1.2, can't be
> claimed to be at fault, right ?

We could call it a missing feature that could lead to a potential bug :)
By your own comment, he "must" was stressed out:
'''
When going into bus suspend/resume we _must_
call gadget driver's ->suspend/->resume callbacks
accordingly. This patch implements that very feature
which has been missing forever.
'''

Since v3.14 is a LTS kernel and the changes are safe, it's worth to
consider.

> 
> I'll leave the final decision to Greg and I don't really oppose having
> both patches on v3.14-stable, but this is not a bug fix in my view.

Thanks. I appreciate your feedback.

BR, David

PS: FWIW implementing features or fixing bugs aren't much different tasks:
https://geekwhisperin.files.wordpress.com/2009/09/bug-vs-feature.jpg
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