linux-kernel - Re: [PATCH 2/8] power: add power sequence library

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Message-ID: <20170201080817.GD17968@kroah.com>
Date:   Wed, 1 Feb 2017 09:08:17 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Peter Chen <peter.chen@....com>,
        Alan Stern <stern@...land.harvard.edu>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Sebastian Reichel <sre@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>, p.zabel@...gutronix.de,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Pawel Moll <pawel.moll@....com>,
        Mark Rutland <mark.rutland@....com>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        mail@...iej.szmigiero.name, troy.kisky@...ndarydevices.com,
        Fabio Estevam <festevam@...il.com>, oscar@...andei.net,
        Stephen Boyd <stephen.boyd@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Joshua Clayton <stillcompiling@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        mka@...omium.org, Vaibhav Hiremath <vaibhav.hiremath@...aro.org>,
        Gary Bisson <gary.bisson@...ndarydevices.com>,
        hverkuil@...all.nl, Krzysztof Kozlowski <krzk@...nel.org>
Subject: Re: [PATCH 2/8] power: add power sequence library

On Wed, Feb 01, 2017 at 12:10:17AM +0100, Rafael J. Wysocki wrote:
> On Tue, Jan 3, 2017 at 7:33 AM, Peter Chen <peter.chen@....com> wrote:
> > We have an well-known problem that the device needs to do some power
> > sequence before it can be recognized by related host, the typical
> > example like hard-wired mmc devices and usb devices.
> >
> > This power sequence is hard to be described at device tree and handled by
> > related host driver, so we have created a common power sequence
> > library to cover this requirement. The core code has supplied
> > some common helpers for host driver, and individual power sequence
> > libraries handle kinds of power sequence for devices. The pwrseq
> > librares always need to allocate extra instance for compatible
> > string match.
> >
> > pwrseq_generic is intended for general purpose of power sequence, which
> > handles gpios and clocks currently, and can cover other controls in
> > future. The host driver just needs to call of_pwrseq_on/of_pwrseq_off
> > if only one power sequence is needed, else call of_pwrseq_on_list
> > /of_pwrseq_off_list instead (eg, USB hub driver).
> >
> > For new power sequence library, it can add its compatible string
> > to pwrseq_of_match_table, then the pwrseq core will match it with
> > DT's, and choose this library at runtime.
> >
> > Signed-off-by: Peter Chen <peter.chen@....com>
> > Tested-by: Maciej S. Szmigiero <mail@...iej.szmigiero.name>
> > Tested-by Joshua Clayton <stillcompiling@...il.com>
> > Reviewed-by: Matthias Kaehlcke <mka@...omium.org>
> > Tested-by: Matthias Kaehlcke <mka@...omium.org>
> 
> Quite honestly, I have a really hard time with trying to follow this
> code and the total lack of documentation makes it even harder.  In
> particular, the generic power sequence code is not even commented at
> all, so it really is hard to say how this is going to work, let alone
> deciding whether or not to apply it.
> 
> Plus, of course, the USB core changes must be acked by the maintainer
> thereof for me to be able to handle the series.

Ah crap, I wanted you to explain it as I too couldn't figure it out :)

> But at this point I basically need you to explain the design to me, please.

Same here.

thanks,

greg k-h