linux-kernel - Re: [PATCH v4 1/3] Runtime Interpreted Power Sequences

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Date:	Thu, 16 Aug 2012 21:49:02 +0200
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Alexandre Courbot <acourbot@...dia.com>,
	Stephen Warren <swarren@...dia.com>,
	Simon Glass <sjg@...omium.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Anton Vorontsov <cbou@...l.ru>,
	David Woodhouse <dwmw2@...radead.org>,
	Arnd Bergmann <arnd@...db.de>,
	Leela Krishna Amudala <leelakrishna.a@...il.com>,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fbdev@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 1/3] Runtime Interpreted Power Sequences

On Thu, Aug 16, 2012 at 12:38:33PM -0600, Stephen Warren wrote:
> On 08/16/2012 12:08 AM, Alexandre Courbot wrote:
> > diff --git a/Documentation/power/power_seq.txt b/Documentation/power/power_seq.txt
> 
> > +Usage by Drivers and Resources Management
> > +-----------------------------------------
> > +Power sequences make use of resources that must be properly allocated and
> > +managed. The power_seq_build() function builds a power sequence from the
> > +platform data. It also takes care of resolving and allocating the resources
> > +referenced by the sequence if needed:
> > +
> > +  struct power_seq *power_seq_build(struct device *dev, struct list_head *ress,
> > +                                    struct platform_power_seq *pseq);
> > +
> > +The 'dev' argument is the device in the name of which the resources are to be
> > +allocated.
> > +
> > +The 'ress' argument is a list to which the resolved resources are appended. This
> > +avoids allocating a resource referenced in several power sequences multiple
> > +times.
> 
> I see in other parts of the thread, there has been discussion re:
> needing the separate ress parameter, and requiring the driver to pass
> this in to multiple power_seq_build calls.
> 
> The way the pinctrl subsystem solved this was to have a single function
> that parsed all pinctrl setting (c.f. all power sequences) at once, and
> return a single handle. Later, the driver passes this handle
> pinctrl_lookup_state(), along with the requested state (c.f. sequence
> name) to search for, and finally passes that handle to
> pinctrl_select_state(). Doing something similar here would result in:
> 
> struct power_seqs *power_seq_get(struct device *dev);
> void power_seq_put(struct power_seqs *seqs);
> struct power_seq *power_seq_lookup(struct power_seqs *seqs,
> 				const char *name);
> int power_seq_executestruct power_seq *seq);
> 
> struct power_seqs *devm_power_seq_get(struct device *dev);
> void devm_power_seq_put(struct power_seqs *seqs);

Hehe, this looks very much like what I had in mind when I proposed this
during the last version of this series. The nice thing about this is
that the API is very much in line with how other subsystems work.

Thierry

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