topic device tree with variable number of cpu in i.MX Processors

device tree with variable number of cpu

niklasmolin — Tue, 24 Feb 2015 23:19:06 GMT

Hi.

If I have an image I want to be able to run in either IMX6Q (4 cores) or IMX6D (2 cores).

Is there a way for the Linux kernel to adjust after number of cores the CPU has or do I need to compile to different images?

In the device tree (for SabreSD there is some configurations for the CPUs, imx6q.dtsi):

cpus {

#address-cells = <1>;

#size-cells = <0>;

cpu0: cpu@0 {

compatible = "arm,cortex-a9";

device_type = "cpu";

reg = <0>;

next-level-cache = <&L2>;

operating-points = <

/* kHz uV */

1200000 1275000

996000 1250000

852000 1250000

792000 1150000

396000 975000

fsl,soc-operating-points = <

/* ARM kHz SOC-PU uV */

1200000 1275000

996000 1250000

852000 1250000

792000 1175000

396000 1175000

clock-latency = <61036>; /* two CLK32 periods */

clocks = <&clks 104>, <&clks 6>, <&clks 16>,

<&clks 17>, <&clks 170>;

clock-names = "arm", "pll2_pfd2_396m", "step",

"pll1_sw", "pll1_sys";

arm-supply = <&reg_arm>;

pu-supply = <&reg_pu>;

soc-supply = <&reg_soc>;

};

cpu@1 {

compatible = "arm,cortex-a9";

device_type = "cpu";

reg = <1>;

next-level-cache = <&L2>;

};

cpu@2 {

compatible = "arm,cortex-a9";

device_type = "cpu";

reg = <2>;

next-level-cache = <&L2>;

};

cpu@3 {

compatible = "arm,cortex-a9";

device_type = "cpu";

reg = <3>;

next-level-cache = <&L2>;

};

Thanks,

Niklas

Re: device tree with variable number of cpu

SergioSolis — Tue, 03 Mar 2015 16:00:49 GMT

Hello Niklas,

Are you referring to have the ability to disable/enable cores "on the fly"?

Re: device tree with variable number of cpu

niklasmolin — Tue, 03 Mar 2015 16:58:21 GMT

Hi Sergio.

It's more to not have to recompile the linux image if I want to run it on a both a IMX6Q and IMX6D.

I haven't tried to see what happens if I compile it for 4 CPUs and run it on a IMX6D.

Re: device tree with variable number of cpu

gfine — Tue, 03 Mar 2015 17:42:52 GMT

Hi Niklas,

You'd be better off adding 'maxcpus=' to the kernel command line in u-boot. No recompiling necessary.

Cheers,

Glen

Re: device tree with variable number of cpu

niklasmolin — Tue, 03 Mar 2015 18:22:48 GMT

Hi Glen.

Thanks for the information.

I should have a check in the u-boot which type of CPU it is and then just set the maxcpus= when I start kernel.

Re: device tree with variable number of cpu

gfine — Tue, 03 Mar 2015 19:28:05 GMT

Hi Niklas,

I think the code isalready there as u-boot.imx is usable across most of the i.MX6 series (except 6Solo). So there may not even be a need to use maxcpus. Only use maxcpus if you need a 6Q to act like a 6D.

Your initial question was if there was a way to do this without recompiling the kernel or the device tree, and that is what the 'maxcpus' kernel command is usually used for. Otherwise u-boot.imx should suffice.

Cheers,

Glen