linux-kernel - Re: [PATCH RFC V1 2/3] rtc: da9063: Add DA9062 RTC capability to DA9063 RTC driver

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Message-ID: <20150721083905.GB2853@piout.net>
Date:	Tue, 21 Jul 2015 10:39:05 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	"Opensource [Steve Twiss]" <stwiss.opensource@...semi.com>
Cc:	Lee Jones <lee.jones@...aro.org>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	DEVICETREE <devicetree@...r.kernel.org>,
	LINUXINPUT <linux-input@...r.kernel.org>,
	LINUXKERNEL <linux-kernel@...r.kernel.org>,
	RTCLINUX <rtc-linux@...glegroups.com>,
	David Dajun Chen <david.chen@...semi.com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Support Opensource <Support.Opensource@...semi.com>
Subject: Re: [PATCH RFC V1 2/3] rtc: da9063: Add DA9062 RTC capability to
 DA9063 RTC driver

Hi,

On 21/07/2015 at 08:05:32 +0000, Opensource [Steve Twiss] wrote :
> > > > > +
> > > > > +	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
> > > > > +	if (!rtc)
> > > > > +		return -ENOMEM;
> > > > > +
> > > > > +	if (strncmp(match->name, "dlg,da9063-rtc", 14) == 0) {
> > > > > +		struct da9063 *chip = dev_get_drvdata(pdev->dev.parent);
> > > > > +
> > > > > +		if (chip->variant_code == PMIC_DA9063_AD)
> > > > > +			rtc->config = &da9063_ad_regs;
> > > > > +	} else
> > > > > +		rtc->config = match->data;
> > > >
> > > > You must not do that.
> > > > You should add a new compatible and change the of_compatible string of
> > > > the mfd_cell in drivers/mfd/da9063-core.c onc you know the variant.
> > >
> > > I can check for a binary comparison against the address of the
> > > static const struct of_device_id da9063_compatible_reg_id_table[] = {}
> > > entry for DA9063.
> > 
> > You also must not compare pointers that way. You can use
> > of_device_is_compatible().
> > 
> > > The DA9063 driver already associates "dlg,da9063-rtc" with both BB and AD
> > > register maps. I think that altering the string at this point would break backwards
> > > compatibility in the device tree for the DA9063.
> > 
> > I'm not fond of the backward compatibility exactly for that kind of
> > issue. The proper way to handle it is to have tow different compatible
> > strings because obviously, the BB and AD variants are not compatible.
> 
> I think I understand what you are saying about modifying the mfd_cell in the
> DA9063 core driver at run-time so that it changes the of_compatible string to [something like]
> "dlg,da9063-ad-rtc". That way the RTC driver can be probed using the correct
> string.
> 
> Ok, I think I see now .. I'll make a patch v2 and send it soon.
> 

This is not needed if you simply change your strncmp with
of_device_is_compatible

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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