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

From: NeilBrown <neilb@suse.com>
To: Mark Brown <broonie@kernel.org>
Cc: Baolin Wang <baolin.wang@linaro.org>,
	Felipe Balbi <balbi@kernel.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	Sebastian Reichel <sre@kernel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>,
	David Woodhouse <dwmw2@infradead.org>,
	robh@kernel.org, Jun Li <jun.li@nxp.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Ruslan Bilovol <ruslan.bilovol@gmail.com>,
	Peter Chen <peter.chen@freescale.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	grygorii.strashko@ti.com,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
	Lee Jones <lee.jones@linaro.org>,
	John Stultz <john.stultz@linaro.org>,
	Charles Keepax <ckeepax@opensource.wolfsonmicro.com>,
	patches@opensource.wolfsonmicro.com,
	Linux PM list <linux-pm@vger.kernel.org>,
	USB <linux-usb@vger.kernel.org>,
	device-mainlining@lists.linuxfoundation.org,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v18 0/4] Introduce usb charger framework to deal with the usb gadget power negotation
Date: Thu, 17 Nov 2016 17:46:13 +1100	[thread overview]
Message-ID: <87fumqhadm.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <20161116161605.smif6kf3mdhdhyhd@sirena.org.uk>

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On Thu, Nov 17 2016, Mark Brown wrote:

> [ Unknown signature status ]
> On Tue, Nov 15, 2016 at 08:35:13AM +1100, NeilBrown wrote:
>> On Mon, Nov 14 2016, Mark Brown wrote:
>
>> > Conflating the two seems like the whole point here.  We're looking for
>> > something that sits between the power supply code and the USB code and
>> > tells the power supply code what it's allowed to do which is the result
>> > of a combination of physical cable detection and USB protocol.  It seems
>> > reasonable that extcon drivers ought to be part of this but it doesn't
>> > seem like they are the whole story.
>
>> I don't think "between the power supply code and the USB code" is where
>> this thing sits. I think it sits inside the power-supply driver.
>> We already have extcon which sits between the phy and the power_supply
>> code, and the usb_notifier which sits between the USB code and the
>> power supply code.  We don't need another go-between.
>
> ...
>
>> correct determinations and set the current limits itself.  All this
>> could be done entirely internally, without the help of any new
>> subsystem.
>> Do you agree?
>
>> Clearly doing it that way would result in lots of code duplication and
>> would mean that each driver probably gets its own private set of bugs,
>> but it would be possible.  Just undesirable.
>
> I think this is the key here - the fact that it's technically possible
> to implement doesn't really matter if it's sufficiently fiddly and non
> obvious that nobody is actually joining everything up (bits are done
> intermittently but not as a whole as far as I can see).
>
>> So yes, it makes perfect to provide common code which handles the
>> registrations, and captures the events, and translates the different
>> events into current levels and feeds those back to the driver.  This
>> isn't some new subsystem, this is just a resource, provided by a
>> library, that power drivers can allocate and initialize if the want to.
>
> To me that's pretty much what's being done here, the code just happens
> to sit in USB instead but fundamentally it's just a blob of helper code,
> you could replace the notifier with a callback if that's the big concern
> here.

It is a lot more than "just a blob of helper code".  It duplicates
existing infrastructure instead of fixing and using the
infrastructure.... but I've said all this before.  Repeatedly.

NeilBrown

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