Intel NUC enable IRQ sharing on serial driver

Product support balenaOS
1

Hello,

I’m on a Intel board, using the Intel NUC image 2.46.0+rev1. I have a 6 serial com ports of which I can only use the first two at the moment. I’d like to be able to use all 6.

I think these dmesg lines are relevant:

[    0.399138] Serial: 8250/16550 driver, 32 ports, IRQ sharing disabled
[    0.420391] 00:01: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A
[    0.441677] 00:02: ttyS1 at I/O 0x2f8 (irq = 3, base_baud = 115200) is a 16550A
[    0.462953] 00:03: ttyS2 at I/O 0x3e8 (irq = 7, base_baud = 115200) is a 16550A
[    0.484225] 00:04: ttyS3 at I/O 0x2e8 (irq = 7, base_baud = 115200) is a 16550A
[    0.505501] 00:05: ttyS4 at I/O 0x2f0 (irq = 7, base_baud = 115200) is a 16550A
[    0.526777] 00:06: ttyS5 at I/O 0x2e0 (irq = 7, base_baud = 115200) is a 16550A
[    0.527712] Linux agpgart interface v0.103

I think the problem is that the last 4 COM ports all share IRQ 7 but IRQ sharing is disabled in the serial driver.
I checked in the BIOS, I can’t assign different IRQ’s to the last 4 COM ports.
My question is; How do I enable IRQ sharing on the 8250 serial driver?

Cheers,
Erik

4

Hi Eric,
At the moment you will need to build your own OS image for the Intel NUC and make the configuration changes yourself. Build instructions can be found at https://www.balena.io/os/docs/custom-build/#Bake-your-own-Image.
The kernel needs to be configured with the CONFIG_SERIAL_8250_EXTENDED and CONFIG_SERIAL_8250_SHARE_IRQ variables. This can be done at https://github.com/balena-os/balena-intel/blob/master/layers/meta-balena-genericx86/recipes-kernel/linux/linux-yocto_%.bbappend. There are some examples of other configurations in that file that can be used as reference.
Let us know how it goes,

6

Hi again Eric, we have opened an issue to add this to meta-balena (https://github.com/balena-os/meta-balena/issues/1815) please track it for the patch availability.

8

Hi Alex,

Thank you for the pointers. To be honest it’s a bit more involved than I’d hoped for but I’ll see how far I’ll get.

Cheers,
Erik