linux-kernel - Re: [PATCH Resend V2] dt: add helper function to read u8 & u16 variables & arrays

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Date:	Sun, 11 Nov 2012 13:42:03 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	rob.herring@...xeda.com, grant.likely@...retlab.ca,
	linaro-dev@...ts.linaro.org, andriy.shevchenko@...el.com,
	patches@...aro.org, devicetree-discuss@...ts.ozlabs.org,
	spear-devel@...t.st.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH Resend V2] dt: add helper function to read u8 & u16 variables
 & arrays

On 11/11/2012 11:27 AM, Viresh Kumar wrote:
> On 11 November 2012 19:42, Rob Herring <robherring2@...il.com> wrote:
>> On 11/06/2012 10:22 PM, viresh kumar wrote:
> 
>>>                 cluster0: cluster@0 {
>>> +                       data1 = <0x50 0x60 0x70>;
>>> +                       data2 = <0x5000 0x6000 0x7000>;
>>> +                       data3 = <0x50000000 0x60000000 0x70000000>;
>>
>> So there is a mismatch in our assumptions. You are just truncating
>> 32-bit values. I assumed you were using the 8 and 16 bit sizes that are
>> now supported in dts. I don't think we should just truncate values
>> blindly. We have support for specifying 8 and 16 values now so you
>> should use that and define that as part of a binding.
> 
> Sorry couldn't get your point at all :(
> What did you mean by "truncating 32 bit values" and how should we
> tell via DT, that the value passed is 8 bit, 16 bit or 32 bit?
> 

You are trying to retrieve an array of 8 or 16-bit values which are
stored as 32-bit values in dtb. Why not define them in the binding as 8
or 16 bit to begin with. Then there is never any ambiguity about their size.

I don't think the size is stored in the dtb. It is only in the dts. You
need to define the size in the binding definitions and use '/bits/'
annotation. With this the data is packed. Then the array function used
should match what the binding defines.

Rob

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