linux-kernel - Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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Message-ID: <87oa3qz7zr.fsf@notabene.neil.brown.name>
Date:   Wed, 14 Sep 2016 19:50:00 +0200
From:   NeilBrown <neilb@...e.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Baolin Wang <baolin.wang@...aro.org>,
        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>, r.baldyga@...sung.com,
        grygorii.strashko@...com,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Lee Jones <lee.jones@...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>,
        "Bird\, Timothy" <Tim.Bird@...sony.com>
Subject: Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

On Wed, Sep 14 2016, Mark Brown wrote:

> TI do a lot of the more software managed chargers (which I suspect are
> the main thing Felipe will have looked at) if that's what you're
> referring to here?  The device is implementing pretty much the algorithm
> you're describing in that e-mail so I'm a bit confused as to what you're
> saying here.

Ah.... my mistake, sorry.
When earlier you said:
>                                                                 It's a
> current limiter intended to sit in line with the USB power lines to
> ensure the system doesn't go over the maximum current draw (and also
> integrates with the power source selection logic the chip has to pick
> the best available power source for the system).

I assumed that all it did was limit the current to number given.
If it also limits the current to ensure that voltage doesn't drop
unduly, then I agree with your assertion that it just needs to be told
the upper limit.
I hope you'll agree that other drivers might need to know the lower
limit, so reporting both to all drivers is sensible.

Thanks,
NeilBrown

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