linux-kernel - Re: [PATCH 02/11] devicetree: bindings: Document Qualcomm cpus and enable-method

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Message-Id: <1A27B0E2-FB92-488D-A0B3-65E677525720@codeaurora.org>
Date:	Tue, 5 Nov 2013 11:43:59 -0600
From:	Kumar Gala <galak@...eaurora.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Rob Herring <robherring2@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	David Brown <davidb@...eaurora.org>,
	Rohit Vaswani <rvaswani@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/11] devicetree: bindings: Document Qualcomm cpus and enable-method


On Nov 5, 2013, at 11:35 AM, Stephen Boyd wrote:

> On 11/05/13 09:12, Kumar Gala wrote:
>> On Nov 4, 2013, at 11:36 AM, Stephen Boyd wrote:
>> 
>>> On 11/01, Rob Herring wrote:
>>>> On Fri, Nov 1, 2013 at 5:08 PM, Stephen Boyd <sboyd@...eaurora.org> wrote:
>>>>> From: Rohit Vaswani <rvaswani@...eaurora.org>
>>>>> 
>>>>> Scorpion and Krait are Qualcomm cpus. These cpus don't use the
>>>>> spin-table enable-method. Instead they rely on mmio register
>>>>> accesses to enable power and clocks to bring CPUs out of reset.
>>>>> 
>>>>> Cc: <devicetree@...r.kernel.org>
>>>>> Signed-off-by: Rohit Vaswani <rvaswani@...eaurora.org>
>>>>> [sboyd: Split off into separate patch, renamed method to
>>>>> qcom,mmio]
>>>>> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
>>>>> ---
>>>>> 
>>>>> This slightly conflicts with my krait EDAC series.
>>>>> 
>>>>> Documentation/devicetree/bindings/arm/cpus.txt | 3 +++
>>>>> 1 file changed, 3 insertions(+)
>>>>> 
>>>>> diff --git a/Documentation/devicetree/bindings/arm/cpus.txt b/Documentation/devicetree/bindings/arm/cpus.txt
>>>>> index 37258f9..e2969fa2 100644
>>>>> --- a/Documentation/devicetree/bindings/arm/cpus.txt
>>>>> +++ b/Documentation/devicetree/bindings/arm/cpus.txt
>>>>> @@ -44,6 +44,8 @@ For the ARM architecture every CPU node must contain the following properties:
>>>>>               "marvell,mohawk"
>>>>>               "marvell,xsc3"
>>>>>               "marvell,xscale"
>>>>> +               "qcom,scorpion"
>>>>> +               "qcom,krait"
>>>>> 
>>>>> And the following optional properties:
>>>>> 
>>>>> @@ -52,6 +54,7 @@ And the following optional properties:
>>>>>                different types of cpus.
>>>>>                This should be one of:
>>>>>                "spin-table"
>>>>> +                "qcom,mmio"
>>>> Not exactly specific. How would you handle variations in the enable
>>>> method? The mmio method to enable is tied to the core type or SOC
>>>> type?
>>> Variations in the enable method are handled by searching for
>>> another node with different compatible strings. Later on in this
>>> series you'll see that we search for gcc-8660, kpss-acc-v1, or
>>> kpps-acc-v2. Once we find one of these nodes we perform the
>>> correct cold boot routine.
>>> 
>>> I'm actually considering renaming this to "qcom,cold-boot". We
>>> could further extend the enable-metho property to allow
>>> "qcom,warm-boot" and then for cases like kexec we could make the
>>> enable method be warm boot and our smp code could be smart enough
>>> to know to skip the whole cold boot sequence.
>> 
>> I think this should be more specific than just 'qcom,mmio' or 'qcom,warm-boot'.  It should be 'qcom,kpss-acc-v1' or 'qcom-gcc-8660'.
>> 
> 
> Do you have any reasons why? I don't see why we need to keep adding more
> and more enable-methods every time the subsystem surrounding the CPU
> changes. The method is the same, write some registers to power up the
> CPU for the first time (cold boot) or ping the CPU to wake it up
> (warmboot). The only difference is where those registers live and a
> slight variation in the sequence that we perform.

By that argument every device could just be compatible with 'mmio' and be done with it ;)

As the registers you write vary, the compatible should vary.

- 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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