linux-kernel - Re: [PATCH v7 2/8] power: add power sequence library

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Date:   Thu, 13 Oct 2016 09:04:42 +0200
From:   Heiko Stuebner <heiko@...ech.de>
To:     Peter Chen <hzpeterchen@...il.com>
Cc:     Peter Chen <peter.chen@....com>, gregkh@...uxfoundation.org,
        stern@...land.harvard.edu, ulf.hansson@...aro.org,
        broonie@...nel.org, sre@...nel.org, robh+dt@...nel.org,
        shawnguo@...nel.org, dbaryshkov@...il.com, dwmw3@...radead.org,
        k.kozlowski@...sung.com, linux-arm-kernel@...ts.infradead.org,
        p.zabel@...gutronix.de, devicetree@...r.kernel.org,
        pawel.moll@....com, mark.rutland@....com,
        linux-usb@...r.kernel.org, arnd@...db.de, s.hauer@...gutronix.de,
        mail@...iej.szmigiero.name, troy.kisky@...ndarydevices.com,
        festevam@...il.com, oscar@...andei.net, stephen.boyd@...aro.org,
        linux-pm@...r.kernel.org, stillcompiling@...il.com,
        linux-kernel@...r.kernel.org, mka@...omium.org,
        vaibhav.hiremath@...aro.org
Subject: Re: [PATCH v7 2/8] power: add power sequence library

Am Donnerstag, 13. Oktober 2016, 09:22:16 CEST schrieb Peter Chen:
> On Wed, Oct 12, 2016 at 12:30:29PM +0200, Heiko Stuebner wrote:
> > Hi,
> > 
> > Am Dienstag, 20. September 2016, 11:36:41 CEST schrieb Peter Chen:
> > > 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.
> > > 
> > > pwrseq_generic is intended for general purpose of power sequence, which
> > > handles gpios and clocks currently, and can cover regulator and pinctrl
> > > 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).
> > > 
> > > Signed-off-by: Peter Chen <peter.chen@....com>
> > > Tested-by Joshua Clayton <stillcompiling@...il.com>
> > > Reviewed-by: Matthias Kaehlcke <mka@...omium.org>
> > > Tested-by: Matthias Kaehlcke <mka@...omium.org>
> > 
> > first of all, glad to see this move forward. I've only some qualms with
> > the
> > static number of allocated power sequences below.
> 
> Thanks for commenting it, the preallocate way is not a good way, but I
> can't find suitable way. See below comments.
> 
> > > +static int __init pwrseq_generic_register(void)
> > > +{
> > > +	struct pwrseq_generic *pwrseq_gen;
> > > +	int i;
> > > +
> > > +	for (i = 0; i < CONFIG_PWRSEQ_GENERIC_INSTANCE_NUMBER; i++) {
> > > +		pwrseq_gen = kzalloc(sizeof(*pwrseq_gen), GFP_KERNEL);
> > > +		if (!pwrseq_gen)
> > > +			return -ENOMEM;
> > > +
> > > +		pwrseq_gen->pwrseq.pwrseq_of_match_table = generic_id_table;
> > > +		pwrseq_gen->pwrseq.get = pwrseq_generic_get;
> > > +		pwrseq_gen->pwrseq.on = pwrseq_generic_on;
> > > +		pwrseq_gen->pwrseq.off = pwrseq_generic_off;
> > > +		pwrseq_gen->pwrseq.put = pwrseq_generic_put;
> > > +		pwrseq_gen->pwrseq.free = pwrseq_generic_free;
> > > +
> > > +		pwrseq_register(&pwrseq_gen->pwrseq);
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +postcore_initcall(pwrseq_generic_register)
> > 
> > I see that you need to have it preallocated for the compatible matching,
> > but wouldn't it also work to either just register the type and allocate
> > dynamically or otherwise just allocate a new spare everytime
> > pwrseq_generic_get() picks up the previous spare?
> 
> Before compatible matching, the host driver doesn't know which pwrseq type
> for its child node, then doesn't know which pwrseq instance needs to be
> allocated. From dts, we don't know which pwrseq type for the node.

yes, that is why I was suggesting allocating one (or two) here in 
pwrseq_generic_register() and every time pwrseq_generic_get() grabs the last 
free sequence instance, you allocate a new free spare one in that function.