What about RT linux?

Hi, radxa team and RockPi4 users :slight_smile:

I want to make a custom OS build with kernel patched by the RT-PREEMPT patch. What the best way to do that?

I saw original rockchip-linux repo has the develop-4.4-rt176 branch. Offcourse, this branch has no latest commits from the radxa’s release-4.4-rockpi4 branch.

Is it possible to use develop-4.4-rt176 branch while building the custom OS image using https://github.com/radxa/rockchip-bsp? Or I must to apply the RT-PREEMPT patch manually to the radxa’s release-4.4-rockpi4?

Similar unanswered topic - PREEMPT-RT Kernel

You can try to apply the ROCK Pi 4 patches from the release-4.4-rockpi4 branch to the develop-4.4-rt176 branch. I think there will not be much conflicts. Or you can just copy the ROCK Pi 4 device tree and build in the develop-4.4-rt176 branch. It should work.

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Thanks. I will try these methods soon and will report about my results.

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@MX_Master, just curious if you did get the develop-4.4-rt176 kernel up and running? I am currently without a Rock Pi 4 to test it on, so all I can do is verify that kernel and image build correctly.

Don’t have any RockPi4 boards yet :slight_smile: I can confirm the develop-4.4-rt176 branch build is successful. I’ll test it when my first board will arrive to me :smile:

You can also try the latest upstream kernel. At least on my board this works out of the box. I haven’t tested all features though. But I guess that a proper patched upstream RT kernel should work as well.

Switching to a mainline kernel would entail porting some of the Rockchip specific drivers (e.g. ap6256 / bcm43456). On the other hand, the Rockchip kernel has some quirks like hidden dependencies (i.e. call dependencies not reflected in Kconfig) that make tailoring it rather difficult.

The first 5.x.y branch to appear in linux-stable-rt would probably be a good starting point.

mainline ap6256 patch is sent recently.

https://lkml.org/lkml/2019/5/28/911

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Thank you @jack! And will brcmfmac support the chip? Linux Wireless lists only BCM43455 at the moment.

BCM43455 and BCM43456 can use the same driver, the difference should be only the firmware. Actually the firmware of BCM43455 can work on BCM43456.

But we actually haven’t tested the wifi/bt on 5.2 kernel yet.