Re: [Patch V2 4/4] ARM: dts: AM33XX: update rtc node compatibility

From: Mark Rutland <mark.rutland@arm.com>
To: Gururaja Hebbar <gururaja.hebbar@ti.com>
Cc: "davinci-linux-open-source@linux.davincidsp.com"
	<davinci-linux-open-source@linux.davincidsp.com>,
	"tony@atomide.com" <tony@atomide.com>,
	"benoit.cousson@gmail.com" <benoit.cousson@gmail.com>,
	Sekhar Nori <nsekhar@ti.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"vaibhav.bedia@ti.com" <vaibhav.bedia@ti.com>,
	"benoit.cousson@linaro.org" <benoit.cousson@linaro.org>,
	"linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
	"devicetree-discuss@lists.ozlabs.org"
	<devicetree-discuss@lists.ozlabs.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [Patch V2 4/4] ARM: dts: AM33XX: update rtc node compatibility
Date: Fri, 2 Aug 2013 13:40:33 +0100	[thread overview]
Message-ID: <20130802124033.GL2884@e106331-lin.cambridge.arm.com> (raw)
In-Reply-To: <51FB9C77.3090202@ti.com>

On Fri, Aug 02, 2013 at 12:48:07PM +0100, Gururaja Hebbar wrote:
> On 8/2/2013 4:50 PM, Mark Rutland wrote:
> > On Fri, Aug 02, 2013 at 12:07:36PM +0100, Gururaja Hebbar wrote:
> >> On 8/1/2013 10:35 PM, Mark Rutland wrote:
> >>> On Tue, Jul 30, 2013 at 05:21:14PM +0100, Sekhar Nori wrote:
> >>>> On 7/30/2013 8:25 PM, Mark Rutland wrote:
> >>>>> On Tue, Jul 30, 2013 at 06:05:52AM +0100, Gururaja Hebbar wrote:
> >>>>>> Hi,
> >>>>>>
> >>>>>> On 7/3/2013 2:17 PM, Hebbar Gururaja wrote:
> >>>>>>> Since AM33xx  RTC IP has RTC_IRQWAKEEN to support Alarm Wake-up.
> >>>>>>>
> >>>>>>> Update the rtc compatible property to "ti,am3352-rtc" to enable handling
> >>>>>>> of this feature inside rtc-omap driver.
> >>>>>>
> >>>>>> The other 2 rtc driver related patches have been pulled up. If you have
> >>>>>> no comments, can you please pull this up.
> >>>>>>
> >>>>>> Regards
> >>>>>> Gururaja
> >>>>>>
> >>>>>>>
> >>>>>>> Signed-off-by: Hebbar Gururaja <gururaja.hebbar@ti.com>
> >>>>>>> ---
> >>>>>>> :100644 100644 77aa1b0... dde180a... M	arch/arm/boot/dts/am33xx.dtsi
> >>>>>>>     arch/arm/boot/dts/am33xx.dtsi |    2 +-
> >>>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>>>>
> >>>>>>> diff --git a/arch/arm/boot/dts/am33xx.dtsi b/arch/arm/boot/dts/am33xx.dtsi
> >>>>>>> index 77aa1b0..dde180a 100644
> >>>>>>> --- a/arch/arm/boot/dts/am33xx.dtsi
> >>>>>>> +++ b/arch/arm/boot/dts/am33xx.dtsi
> >>>>>>> @@ -297,7 +297,7 @@
> >>>>>>>     		};
> >>>>>>>
> >>>>>>>     		rtc@44e3e000 {
> >>>>>>> -			compatible = "ti,da830-rtc";
> >>>>>>> +			compatible = "ti,am3352-rtc";
> >>>>>
> >>>>> Given that this is backwards compatible with the old binding, it would
> >>>>> be nicer to have this as:
> >>>>>
> >>>>> 	compatible = "ti,am3352-rtc", "ti,da830-rtc";
> >>>>>
> >>>>> We must get into the habit of changing dts files in a
> >>>>> backwards-compatible fashion.
> >>>>
> >>>> Right, I suggested this when v1 was posted. It turns out the current
> >>>> kernel does not handle the compatilble list correctly and the string
> >>>> selected actually depends on the order in which it appears in match
> >>>> table in driver instead.
> >>>>
> >>>> I saw there were patches being discussed to fix this issue, but until
> >>>> that is fixed, we cannot really use what you (and I before) suggested.
> >>>
> >>> A temporary solution would be to list the "ti,am3352-rtc" first in the
> >>> of_match_table kernel-side.
> >>
> >> If above method is followed, then it would cause trouble on davinci
> >> platform because this rtc-omap driver is also used by Davinci platform.
> >> On davinci Plaform the driver would match with "ti,am3352-rtc" for
> >> compatible.
> >
> > Sorry, I don't follow. Does the davinci dt have "ti,am3352-rtc" in it's
> > compatible string list?
> 
> no no. Davinci .dts uses "ti,da830-rtc".

Ok.

> 
> I was saying if we reverse the order of "of_device_id" structure in 
> rtc-omap driver, then it would work nicely for am335x but will cause 
> trouble on davinci platform.

I don't understand. If we place "ti,am3352-rtc" first in the list, it
won't be match the davinci dts compatible string, and the code will go
over the of_device_id entires until it finds the "ti,da830-rtc" entry
used by davinci.

What problem would this cause, and why?

Thanks,
Mark.

> 
> >
> > If so, and it's not compatible, the dts is wrong.
> >
> > If not, then we won't use the behaviour specific to "ti,am3352-rtc", and
> > there's no problem.
> >
> > What trouble would this cause?
> >
> > Thanks,
> > Mark.
> >
> >>
> >> Regards
> >> Gururaja
> >>
> >>> That way you can keep the old compatible
> >>> string in the dts compatible list, and maintain backwards compatibilty
> >>> with older kernels.
> >>>
> >>> Later if the way Linux matches compatible strings is changed, this
> >>> shouldn't break the probe order, and the of_match_table order could be
> >>> changed.
> >>>
> >>> Have I missed something?
> >>>
> >>> Thanks,
> >>> Mark.
> >>>
> >>
> >>
> >> _______________________________________________
> >> linux-arm-kernel mailing list
> >> linux-arm-kernel@lists.infradead.org
> >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> >>
> 
> 
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