linux-kernel - Re: [PATCH 1/4] Documentation: Add memory mapped ARM architected timer binding

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Message-ID: <516444FE.2080200@codeaurora.org>
Date:	Tue, 09 Apr 2013 09:42:38 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Mark Rutland <mark.rutland@....com>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	Marc Zyngier <Marc.Zyngier@....com>
Subject: Re: [PATCH 1/4] Documentation: Add memory mapped ARM architected
 timer binding

On 04/09/13 02:08, Mark Rutland wrote:
> On Tue, Apr 09, 2013 at 03:30:20AM +0100, Stephen Boyd wrote:
>>  
>> -** Timer node properties:
>> +** CP15 Timer node properties:
>>  
>>  - compatible : Should at least contain one of
>>  	"arm,armv7-timer"
>> @@ -26,3 +30,55 @@ Example:
>>  			     <1 10 0xf08>;
>>  		clock-frequency = <100000000>;
>>  	};
>> +
>> +** Memory mapped timer node properties
>> +
>> +- compatible : Should at least contain "arm,armv7-timer-mem".
>> +
>> +- #address-cells : Must be 1.
> What about LPAE systems?
>
> How about something like the following:
>
> #address-cells : If the ranges property is empty, the same value as the
>                  parent node's #address-cells property. Otherwise, a
> 		 value such that the ranges property specifies a
> 		 mapping to the parent node's address space.            

Yes that is much better. I wasn't trying to preclude LPAE or 64 bit systems.

>> +
>> +- #size-cells : Must be 1.
>> +
>> +- ranges : Indicates parent and child bus address space are the same.
>> +
> Similarly, what if someone wants to write a more complex mapping for some
> reason?
>
> We should be able to handle it if we use the standard accessors.

Maybe I should just leave this part out? They are standard DT properties
so I could assume DT writers know what to do.

>> +- clock-frequency : The frequency of the main counter, in Hz. Optional.
>> +
>> +- reg : The control frame base address.
>> +
>> +Frame:
>> +
>> +- frame-id: Encoded as follows:
>> +		bits[3:0]  frame number: 0 to 7.
>> +		bits[10:8] frame usage:
>> +			0 - user/kernel
>> +			1 - hyp
>> +			2 - secure
>> +
> Could we not just have a disabled status property for those frames claimed by a
> higher level (either secure firmware or hypervisor)? Or have I missed something
> here?

Using disabled status would work. I was also thinking maybe we should
use a compatible string in each frame's node. Then we could match
against compatible children like "frame-user", "frame-kernel",
"frame-hyp", "frame-secure", "frame-user-kernel", etc. It allows us
flexibility if we should need to add something else in the future.

Also to get the frame number, I was thinking maybe we should expand the
reg property to have two address cells. Then we could have reg = <0
0xf0001000 0x1000>.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation

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