linux-kernel - Re: [PATCH v15 2/7] power: add power sequence library

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Date:   Wed, 14 Jun 2017 09:53:39 +0800
From:   Peter Chen <hzpeterchen@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     Peter Chen <peter.chen@....com>,
        Mark Rutland <mark.rutland@....com>,
        Heiko Stuebner <heiko@...ech.de>,
        Stephen Boyd <stephen.boyd@...aro.org>, <frank.li@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Gary Bisson <gary.bisson@...ndarydevices.com>,
        Fabio Estevam <festevam@...il.com>,
        Joshua Clayton <stillcompiling@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
        Vaibhav Hiremath <vaibhav.hiremath@...aro.org>,
        Krzysztof Kozlowski <krzk@...nel.org>, <mka@...omium.org>,
        Alan Stern <stern@...land.harvard.edu>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>,
        Pawel Moll <pawel.moll@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        <troy.kisky@...ndarydevices.com>, Rob Herring <robh+dt@...nel.org>,
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        <linux-arm-kernel@...ts.infradead.org>, <hverkuil@...all.nl>,
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        Mark Brown <broonie@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>, <jun.li@....com>
Subject: Re: [PATCH v15 2/7] power: add power sequence library

On Tue, Jun 13, 2017 at 12:24:42PM +0200, Ulf Hansson wrote:
> [...]
> 
> > +
> > +/**
> > + * of_pwrseq_on - Carry out power sequence on for device node
> > + *
> > + * @np: the device node would like to power on
> > + *
> > + * Carry out a single device power on.  If multiple devices
> > + * need to be handled, use of_pwrseq_on_list() instead.
> > + *
> > + * Return a pointer to the power sequence instance on success,
> > + * or an error code otherwise.
> > + */
> > +struct pwrseq *of_pwrseq_on(struct device_node *np)
> > +{
> > +       struct pwrseq *pwrseq;
> > +       int ret;
> > +
> > +       pwrseq = pwrseq_find_available_instance(np);
> > +       if (!pwrseq)
> > +               return ERR_PTR(-ENOENT);
> 
> In case the pwrseq instance hasn't been registered yet, then there is
> no way to deal with -EPROBE_DEFER properly here.
> 
> I haven't been following the discussions in-depth during all
> iterations, so perhaps you have already discussed why doing it like
> this.

Yes, it has been discussed. In order to compare with compatible string
at dts, we need to have one registered pwrseq instance for each
pwrseq library, this pre-registered one is allocated using
postcore_initcall, and the new (eg, second) instance is registered
after pwrseq_get has succeeded.

Peter

> 
> Anyway, that means all pwrseq instances needs to be registered an
> early boot level, to be safe. To me, that seems like poor design
> choice.
> 
> Otherwise I think this looks okay to me.
> 

-- 

Best Regards,
Peter Chen