linux-kernel - Re: [PATCH 1/2] pwm: pwm-tiecap: Add device-tree binding support for APWM driver

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Message-ID: <20121008133951.GA26525@avionic-0098.mockup.avionic-design.de>
Date:	Mon, 8 Oct 2012 15:39:51 +0200
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	"Philip, Avinash" <avinashphilip@...com>
Cc:	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"rob@...dley.net" <rob@...dley.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"Nori, Sekhar" <nsekhar@...com>,
	"Hebbar, Gururaja" <gururaja.hebbar@...com>,
	"Hiremath, Vaibhav" <hvaibhav@...com>
Subject: Re: [PATCH 1/2] pwm: pwm-tiecap: Add device-tree binding support for
 APWM driver

On Mon, Oct 08, 2012 at 01:31:19PM +0000, Philip, Avinash wrote:
> On Tue, Oct 02, 2012 at 11:30:14, Thierry Reding wrote:
> > On Wed, Sep 26, 2012 at 04:57:42PM +0530, Philip, Avinash wrote:
[...]
> > > @@ -231,13 +290,56 @@ static int __devinit ecap_pwm_probe(struct platform_device *pdev)
> > >  	}
> > >  
> > >  	pm_runtime_enable(&pdev->dev);
> > > +
> > > +	/*
> > > +	 * Some platform has extra PWM-subsystem common config space
> > > +	 * and requires special handling of clock gating.
> > > +	 */
> > > +	if (pdata && pdata->has_configspace) {
> > > +		r = platform_get_resource(pdev, IORESOURCE_MEM, 1);
> > > +		if (!r) {
> > > +			dev_err(&pdev->dev, "no memory resource defined\n");
> > > +			ret = -ENODEV;
> > > +			goto err_disable_clock;
> > > +		}
> > > +
> > > +		pc->config_base = devm_ioremap(&pdev->dev, r->start,
> > > +				resource_size(r));
> > > +		if (!pc->config_base) {
> > > +			dev_err(&pdev->dev, "failed to ioremap() registers\n");
> > > +			ret = -EADDRNOTAVAIL;
> > > +			goto err_disable_clock;
> > > +		}
> > 
> > Isn't this missing a request_mem_region()? I assume you don't do that
> > here because you need the same region in the EHRPWM driver, right?
> 
> request_mem_region() is avoided as this region is shared across PWM
> sub modules ECAP & EHRPWM. 
> 
> > This should be indication enough that the design is not right here.
> > I think we need a proper abstraction here. Can this not be done via
> > PM runtime support? If not, maybe this should be represented by
> > clock objects since the bit obviously enables a clock.
> 
> It is not done as part of PM runtime as this is has nothing to
> do with clock tree of the SOC. The bits we were enabling here
> should consider as an enable of the individual sub module as
> part of IP integration. Hence we were handling these subsystem
> module enable in the driver itself.

My point remains valid: you shouldn't be able to access the same
register through two different drivers. That's one of the reasons, if
not the only reasen, why the request_mem_region() function exists. I
think you should add some abstraction to provide this functionality to
the drivers. I assume that eventually there will be more than just the
PWM cores that require access to this register.

Thierry

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