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

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Date:	Wed, 3 Jul 2013 13:42:07 +0530
From:	Sekhar Nori <nsekhar@...com>
To:	Sekhar Nori <nsekhar@...com>
CC:	Hebbar Gururaja <gururaja.hebbar@...com>,
	<davinci-linux-open-source@...ux.davincidsp.com>,
	<tony@...mide.com>,
	Benoît Cousson <benoit.cousson@...il.com>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<devicetree-discuss@...ts.ozlabs.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 4/4] ARM: dts: AM33XX: update rtc node compatibility

Gururaja,

On 7/2/2013 11:42 AM, Sekhar Nori wrote:
> Changing to Benoit's gmail id since he apparently wont access TI mail
> anymore.
> 
> On 6/28/2013 3:05 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.
>>
>> Signed-off-by: Hebbar Gururaja <gururaja.hebbar@...com>
>> Cc: Tony Lindgren <tony@...mide.com>
>> Cc: Sekhar Nori <nsekhar@...com>
>> Cc: Kevin Hilman <khilman@...aro.org>
>> Cc: b-cousson@...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";
> 
> compatible is a list so you can instead do:
> 	
> 	compatible = "ti,am3352-rtc", "ti,da830-rtc";
> 
> That way the dts works irrespective of driver updates. When driver
> supports enhanced features of hardware, they are available to the user
> else the basic functionality still works.

On doing some experiments myself, the of_device_id which gets selected
during probe depends on the order in which its entry appears in the
match table inside the driver rather than how the compatible string is
written. I think this puts undue dependency on how the driver is
written, so I am okay with providing a single compatible value like the
way you have done ATM.

I do think the string appearing first in the compatible list is what
should be selected if a match is available but I am not sure if there
are other considerations due to which of_match_device() is written the
way it is written.

Thanks,
Sekhar
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