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

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Date:	Fri, 2 Aug 2013 16:37:36 +0530
From:	Gururaja Hebbar <gururaja.hebbar@...com>
To:	Mark Rutland <mark.rutland@....com>
CC:	Sekhar Nori <nsekhar@...com>,
	"davinci-linux-open-source@...ux.davincidsp.com" 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	"tony@...mide.com" <tony@...mide.com>,
	"benoit.cousson@...il.com" <benoit.cousson@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"vaibhav.bedia@...com" <vaibhav.bedia@...com>,
	"benoit.cousson@...aro.org" <benoit.cousson@...aro.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Patch V2 4/4] ARM: dts: AM33XX: update rtc node compatibility

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@...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@...3e000 {
>>>>> -			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.

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.
>

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