linux-kernel - Re: [PATCH v18 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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Message-ID: <20161028170302.au73yu2fplfig36a@sirena.org.uk>
Date:   Fri, 28 Oct 2016 18:03:02 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     NeilBrown <neilb@...e.com>, Felipe Balbi <balbi@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Sebastian Reichel <sre@...nel.org>,
        Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
        David Woodhouse <dwmw2@...radead.org>, robh@...nel.org,
        Jun Li <jun.li@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Ruslan Bilovol <ruslan.bilovol@...il.com>,
        Peter Chen <peter.chen@...escale.com>,
        Alan Stern <stern@...land.harvard.edu>,
        grygorii.strashko@...com,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Lee Jones <lee.jones@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
        patches@...nsource.wolfsonmicro.com,
        Linux PM list <linux-pm@...r.kernel.org>,
        USB <linux-usb@...r.kernel.org>,
        device-mainlining@...ts.linuxfoundation.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v18 0/4] Introduce usb charger framework to deal with the
 usb gadget power negotation

On Fri, Oct 28, 2016 at 08:51:41PM +0800, Baolin Wang wrote:
> On 28 October 2016 at 06:00, NeilBrown <neilb@...e.com> wrote:

> > 1/ I think we agreed that it doesn't make sense for there to be
> >  two chargers registered in a system.

> Yes, until now...

> >  However usb_charger_register() still allows that, and assigns
> >  and arbitrary name to each based on discovery order.
> >  This *cannot* make sense.

> Fine, I can change that to allow only one charger to register.

Yeah, it's a reasonable change.  I'm not sure the prior discussion was
100% conclusive on the issue (I remember there being some debate about
leaving things there to avoid any need for future refactoring to touch
the interface).

> > 2/ Why do you have usb_charger_set_current()??
> >   No code ever calls it.
> >   This updates the min and max current which are defined in a
> >   standard.  It never makes sense to change the min and max
> >   for a particular cable type.

> Mark, do we have some scenarios which want to change the current
> limitation? If not, okay, I agree with you to remove this function.

I'm not aware of any, we can always add it back if the need arises.

> >  Related:  I don't like charger_type_show().  I don't think
> >  the usb-charger should export that information to user-space because
> >  extcon already does that, and duplication is confusing and pointless.

> I think we should combine all charger related information into one
> place for user. Moreover if we don't get charger type from extcon, we
> should also need one place to export the charger type.

I had also thought there was some software negotation as well as the
physical charger in cases where the device is plugged into an active
host?  I could be wrong.

> > 5/ There is no convincing example usage of this framework.
> >   wm8931x_power.c just scratches the surface.
> >   If it is so good, it should be easy to convert a lot of other
> >   drivers over to it.  If you did that it would be much easier
> >   to see how it works and what the strengths/weaknesses were.

> Jun have send out one patchset[1] based on my patchset, and he tested
> mypatchset. Thanks for your comments.
> [1]http://www.spinics.net/lists/linux-usb/msg139809.html

I think it's a good idea to pick up Jun's patches into your patch set,
that way Jun doesn't need to rebase and it might help with review of
your patches too.

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