linux-kernel - Re: [PATCH v2 1/4] mfd: add LP3943 MFD driver

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Date:	Thu, 1 Aug 2013 09:03:31 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	"Kim, Milo" <Milo.Kim@...com>
Cc:	"Samuel Ortiz (sameo@...ux.intel.com)" <sameo@...ux.intel.com>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"thierry.reding@...il.com" <thierry.reding@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] mfd: add LP3943 MFD driver

On Wed, 31 Jul 2013, Kim, Milo wrote:

> Thanks for the review, please see my comments.
> 
> > <snip> * looks good up to me up to here *
> > 
> > Although, I think the 0 = 1, 1 = 2 ... stuff is really confusing. Is
> > there nothing we can do about that?
> 
> OK, enum value of lp3943_pwm_output can be changed as below
> because LP3943_PWM_INVALID is not used anymore.
> 
> enum lp3943_pwm_output {
> 	LP3943_PWM_OUT0,
> 	LP3943_PWM_OUT1,
> 	...
> 	LP3943_PWM_OUT15,
> };
> 
> Then, output index will match each enum integer value.
> Does it make sense?

Not really. IIRC the documentation said that LED0 (which I believe
you're calling OUT0 here) is located at pin one. So your enum above is
now incorrect isn't it? As *_OUT0 will be 0 and not 1? Or am I missing
something?

> > > +static int __init lp3943_init(void)
> > > +{
> > > +	return i2c_add_driver(&lp3943_driver);
> > > +}
> > > +subsys_initcall(lp3943_init);
> > > +
> > > +static void __exit lp3943_exit(void)
> > > +{
> > > +	i2c_del_driver(&lp3943_driver);
> > > +}
> > > +module_exit(lp3943_exit);
> > 
> > I think you want to replace:
> >   lp3943_init()
> >   lp3943_exit
> > 
> > With:
> >   module_i2c_driver()
> 
> This is related with initcall sequence.
> Some problem may happen if any GPIO or PWM consumer tries to request before
> LP3943 MFDs are added.
> For example, a GPIO is requested in _probe() of some device.
> Let's assume the GPIO number is in range of what LP3943 GPIO driver provided.
> Then, gpio_request() will be failed because the GPIO is invalid at this moment.
> If the device request again later, it will be OK, but we can't expect this 
> situation for every driver.
> Some drivers request a GPIO only once in _probe(), other devices may request
> a GPIO in some cases.
> So, I think lp3943_init() should be defined as subsys_initcall() instead of 
> module_init().

No I don't think so. Instead, you should use -EPROBE_DEFER in lieu of
messing around with initialisation orders.

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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