Reverse RefClk patch for Jetpack 5.0.2


I am looking for a Linux kernel patch for reverse RefClk on Jetpack 5.0.2. I have a patch for Jetpack 4.6 (Kernel 4.9.253) which involves plugin-manager. As we don’t have plugin-manager available for Xavier NX for Jetpack 5.0.2. Can anyone please guide me how we can proceed with reverse refclk on Xavier NX?


The patch for JP 4.6 includes the following:

  1. The patch file which shows changes to be done in pcie-tegra.c file.
    pcie-tegra.patch (1.8 KB)

  2. Add a new similar dts file for P3668 (Xavier NX) and add it to makefile.
    tegra194-p2888-0001-p2822-0000-reverse-refclk.dts (1.3 KB)

Can anyone please help me with the patch?

It is uncertain why you need reverse the clock. Could you share more information about the use-case?

Hi @DaneLLL , The Pcie Gen3 switch is in Direct Switch (D-Switch mode) and this will require all the NX in the system to be ROOT port mode and all the NX modules must be connected to PFX using common clocking. To enable this, we need reverse RefClk to be provided all other modules except one. Please let me know if you need more information. The patch I mentioned above was used in JP 4.6 to use this feature.

Plugin manager is to override the original setting. You can apply the setting to device tree of Xavier NX directly. You can check if the setting is correct after booting, by executing xxd. For example:

$ xxd /proc/device-tree/pcie@140a0000/status
00000000: 6469 7361 626c 6564 00                   disabled.

Can you summarize the changes needs to be done ?

We don’t actually have experience about enabling this on L4T releases. Would see if other users can share experience for the porting.

can you please share how to reverse the clock on Jetpack 5.0.2? Do I need to change pcie_tegra.c and device tree file as well?

We would suggest confirm it on Jetpack 4.6. Please not to apply the patch on Jetpack 4.6 to confirm if it is must-have. Ideally you would need to port the same from K4.9 to K5.10.

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