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− | <big> RZ/G2 Kernel and Linux FAQ </big>
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− | __TOC__
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− | = CPU Hotplug =
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− | You can enable and disable CPU cores by writing to a sysfs value.
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− | <br>
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− | This is helpful for when you want to experiment with the performance of your application if you were to use a processor with less CPU cores.
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− | For example, this command will disable the 2nd core.
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− | <code>$ echo 0 > /sys/devices/system/cpu/cpu1/online</code>
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− | More detailed information can be found here: https://www.cyberciti.biz/faq/debian-rhel-centos-redhat-suse-hotplug-cpu
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− | = Power Saving =
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− | * In Linux, this is a mechanism that is generally supported by all kernels.(it may depend on the version)
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− | * The Renesas kernel has support them.
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− | About power consumption in RZ/G2 series, we have some supported features to save power cost in default environment:
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− | * CPUHotplug: Turn on/off CPU in runtime.
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− | * CPUIdle: Support 2 modes to turn off clock or power domain of CPU when CPU is idle (nothing to do).
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− | ** Sleep mode: put in sleep state.
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− | ** Core standby mode: put in shutdown state. It is described in devicetree of each SoC => It has deeper state than sleep mode so that save more power.
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− | * CPUFreq: there are 6 governors to support "Dynamic Frequency Scaling":
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− | ** '''Performance''': The frequency is always set maximum => It is using as default in our current environment.
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− | ** '''Powersave''': The frequency is always set minimum.
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− | ** '''Ondemand''': If CPU load is bigger than 95%, the frequency is set max. If CPU load is equal to or less than 95%, the frequency is set based on CPU load.
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− | ** Conservative: If CPU load is bigger than 80%, the frequency is set one level higher than current frequency. If CPU load is equal to or less than 20%, the frequency is set one level lower than current frequency.
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− | ** '''Userspace''': It sets frequency which is defined by user in runtime.
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− | ** '''Schedutil''': Schedutil governor is driven by scheduler. It uses scheduler-provided CPU utilization information as input for making its decisions by formula: freq_next= 1.25 * freq_max* util_of_CPU.
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− | * Power Domain: it is supported as default by Linux Power Management Framework. If a module is not use, system will disable its clock and power domain automatically.
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− | Therefore, select proper method will be based on user's purpose. Here are my examples:
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− | * Want to use with best performance: disable CPUIdle + use performance frequency governor.
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− | * Want to use less power: enable CPUIdle + use powersave frequency governor.
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− | * Want to balance performance and power: we can use schedutil.
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− | * Want to modify frequency as user's purpose: use userspance frequency governor.
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− | * If user is running realtime environment, I suggest using performance governor to ensure the minimum latency.
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− | Here are some commands to check frequency value and frequency governor in linux:
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− | * Check available CPU frequency:
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− | : <code> cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_available_frequencies </code>
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− | * Check available CPU frequency governor:
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− | : <code>cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_available_governors </code>
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− | * Change to other governor:
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− | : <code>echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor (performance/userspace/schedutil/...) </code>
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− | * Check current frequency:
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− | : <code> cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq</code>
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− | = PMIC Access from Linux =
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− | The easiest way to access the PMIC registers from command line would would be to use i2ctools. Add the following line to your local.conf.
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− | : <code>IMAGE_INSTALL_append = " i2c-tools"</code>
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− | However the PMICs are connected to a I2C (IIC for PMIC or I2C_DVFS) that is not enabled in the default kernel device tree.
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− | For the HiHope boards, you can edit the file <code>arch/arm64/boot/dts/renesas/hihope-common.dtsi</code> and add the following lines at the very bottom of the file.
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− | <pre>
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− | &i2c_dvfs {
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− | status = "okay";
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− | };
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− | </pre>
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− | Once booted in Linux, the corresponding device should be /dev/i2c-7
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− | You can query the connected slaves by giving the following command:
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− | : <code> i2cdetect -y -r 7 </code>
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− | that on the RZ/G2E board produces the output:
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− | <pre>0 1 2 3 4 5 6 7 8 9 a b c d e f
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− | 00: -- -- -- -- -- -- -- -- -- -- -- -- --
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− | 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- 1e 1f
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− | 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
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− | 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
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− | 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
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− | 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
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− | 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
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− | 70: -- -- -- -- -- -- -- -- </pre>
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− | So two slaves, at address 0x1e and 0x1f.
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− | Finally you can read registers by simply using the i2cget command, for example:
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− | <pre>
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− | i2cget -y 7 0x1e 0x1
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− | 0x02
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− | i2cget -y 7 0x1e 0x16
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− | 0x00
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− | i2cget -y 7 0x1e 0x17
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− | 0xc4
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− | </pre>
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− | If you don't want (or can't) update the device tree blob, you could use u-boot to do it temporarily.
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− | The procedure below is valid for RZ/G2M but it works also with RZ/G2E-N-H by simply modifying the device tree blob and/or kernel image names.
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− | 1) Interrupt the normal kernel boot
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− | 2) Once in u-boot, enter the follow commands (after each RESET)
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− | <pre>=> fatload mmc 0:1 0x48080000 Image; fatload mmc 0:1 0x48000000 Image-r8a774a1-hihope-rzg2m-ex.dtb;
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− | => fdt addr 0x48000000
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− | => fdt set /soc/i2c@e60b0000 status "okay"</pre>
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− | and finally boot the kernel:
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− | <pre>=> booti 0x48080000 - 0x48000000 </pre>
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− | = Create a uImage =
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− | In the kernel, there is no make target to make a uImage for the 64-bit ARM architecture like there is for 32-bit ARM.
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− | However, you can manually make one from the file Image.gz that is created by the kernel build system by using the following command on your host machine.
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− | <pre>
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− | $ cd arch/arm64/boot
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− | $ mkimage -A arm64 -O linux -T kernel -C gzip -a 0x48080000 -e 0x48080000 -n "Linux Kernel Image" -d Image.gz uImage
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− | </pre>
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− | Below is an example of booting this image on a RZ/G2 HiHiope board from u-boot.
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− | <pre>
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− | => fatload mmc 0:1 0x88000000 uImage
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− | => fatload mmc 0:1 0x48000000 Image-r8a774e1-hihope-rzg2h-ex.dtb
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− | => bootm 0x88000000 - 0x48000000
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− | </pre>
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