linux-kernel - Re: [PATCH v3 2/4] arm64: dts: Add Qualcomm MSM8916 SoC and evaluation board dts

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Date:	Thu, 12 Mar 2015 14:54:15 -0500
From:	Kumar Gala <galak@...eaurora.org>
To:	Mark Rutland <mark.rutland@....com>
Cc:	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"arm@...nel.org" <arm@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"heiko@...ech.de" <heiko@...ech.de>
Subject: Re: [PATCH v3 2/4] arm64: dts: Add Qualcomm MSM8916 SoC and evaluation board dts


On Mar 12, 2015, at 1:25 PM, Mark Rutland <mark.rutland@....com> wrote:

>>>> +	cpus {
>>>> +		#address-cells = <1>;
>>>> +		#size-cells = <0>;
>>>> +
>>>> +		CPU0: cpu@0 {
>>>> +			device_type = "cpu";
>>>> +			compatible = "arm,cortex-a53", "arm,armv8";
>>>> +			reg = <0x0>;
>>>> +		};
>>>> +
>>>> +		CPU1: cpu@1 {
>>>> +			device_type = "cpu";
>>>> +			compatible = "arm,cortex-a53", "arm,armv8";
>>>> +			reg = <0x1>;
>>>> +		};
>>>> +
>>>> +		CPU2: cpu@2 {
>>>> +			device_type = "cpu";
>>>> +			compatible = "arm,cortex-a53", "arm,armv8";
>>>> +			reg = <0x2>;
>>>> +		};
>>>> +
>>>> +		CPU3: cpu@3 {
>>>> +			device_type = "cpu";
>>>> +			compatible = "arm,cortex-a53", "arm,armv8";
>>>> +			reg = <0x3>;
>>>> +		};
>>>> +	};
>>> 
>>> The secondary CPUs need an enable-method. Are you using PSCI or
>>> spin-table?
>> 
>> This is on purpose.  We aren’t using either PSCI or spin-table.  Right
>> now the dts is for booting on a single core.  I can drop CPU1..CPU3 if
>> that helps.
> 
> We won't poke the CPUs without an enable-method, so personally I'm not
> too worried either way about having the CPUs listed.

That was my thinking, so left them in.

> Which of spin-table/psci are you planning on using for SMP support, and
> when would that be likely to appear?

We have a qcom specific SMP enablement method for this device.  This was one of our first devices so it utilized as much from arm 32-bit as possible.

> Which exception level do CPUs enter the kernel? Even without a
> virt-capable GIC booting at EL2 is less work for the FW and gives the
> kernel a better chance of fixing things up (e.g. CNTVOFF).

I think the enter in EL1.

- k
-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

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