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

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

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