linux-kernel - Re: [PATCH 03/11] devicetree: bindings: Document qcom,kpss-acc

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Message-Id: <716EE5E6-F792-423A-86C3-6251C54683E1@codeaurora.org>
Date:	Fri, 8 Nov 2013 08:30:11 -0600
From:	Kumar Gala <galak@...eaurora.org>
To:	Tomasz Figa <tomasz.figa@...il.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Stephen Boyd <sboyd@...eaurora.org>,
	devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	Rohit Vaswani <rvaswani@...eaurora.org>,
	linux-kernel@...r.kernel.org, David Brown <davidb@...eaurora.org>
Subject: Re: [PATCH 03/11] devicetree: bindings: Document qcom,kpss-acc


On Nov 8, 2013, at 3:10 AM, Tomasz Figa wrote:

> On Tuesday 05 of November 2013 11:51:07 Kumar Gala wrote:
>> On Nov 5, 2013, at 11:44 AM, Stephen Boyd wrote:
>>> On 11/05/13 09:13, Kumar Gala wrote:
>>>> On Nov 1, 2013, at 5:08 PM, Stephen Boyd wrote:
>>>>> diff --git
>>>>> a/Documentation/devicetree/bindings/arm/msm/qcom,kpss-acc.txt
>>>>> b/Documentation/devicetree/bindings/arm/msm/qcom,kpss-acc.txt new
>>>>> file mode 100644
>>>>> index 0000000..ed4a9c8
>>>>> --- /dev/null
>>>>> +++ b/Documentation/devicetree/bindings/arm/msm/qcom,kpss-acc.txt
>>>>> @@ -0,0 +1,21 @@
>>>>> +* Krait Processor Sub-system (KPSS) Application Clock Controller
>>>>> (ACC)
>>>>> +
>>>>> +The KPSS ACC provides clock, power domain, and reset control to a
>>>>> Krait CPU. +There is one ACC register region per CPU within the
>>>>> KPSS remaped region as +well as an alias register region that
>>>>> remaps accesses to the ACC associated +with the CPU accessing the
>>>>> region.
>>>>> +
>>>>> +Required Properties:
>>>>> +
>>>>> +- compatible : Shall contain "qcom,kpss-acc-v1" or
>>>>> "qcom,kpss-acc-v2".
>>>>> +- reg: Specifies the base address and size of the banked register
>>>>> region. +- cpu-offset : per-cpu offset used when the device is
>>>>> accessed without the +		CPU remapping facilities.
>>>>> +		The offset is cpu-offset + (0x10000 * cpu-nr).
>>>>> +
>>>>> +Example:
>>>>> +
>>>>> +	clock-controller@...8000 {
>>>>> +		compatible = "qcom,kpss-acc-v2";
>>>>> +		reg = <0x02008000 0x1000>;
>>>>> +	};
>>>> 
>>>> I don't get the cpu-offset business, shouldn't this just be:
>>>> 	reg = <0x02008000 0x1000>, <0x02018000 0x1000>, <0x02028000 
> 0x1000>,
>>>> 	<0x02038000 0x1000>;> 
>>> (Sorry I forgot to add the cpu-offset to the example.)
>>> 
>>> Your reg property is one way to do it. I was following the example of
>>> the GIC binding which just specifies the alias region of the GIC's CPU
>>> registers and then has a cpu-offset property to describe how to reach
>>> a
>>> specific CPU's region.
>> 
>> Even in the gic's case I think we should have the reg property cover the
>> memory map.
> 
> The GIC case was supposed to be a hack for Exynos SoCs that do not have 
> banked per-CPU registers. Currently I consider it broken, because it does 
> not scale for multi cluster configurations. I believe you should consider 
> the same.
> 
> IMHO the way to provide per-CPU properties should involve CPU nodes to 
> make sure that the same CPU ID namespace is always used.
> 
> Best regards,
> Tomasz


Yeah, Stephen and I talked off line about it and I think we'll end up with a bit of both.  Having the reg property describe both regions, as well as having some nodes via the CPU node to get to the proper "device" for that cpu.

- k

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

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