Re: [PATCH] serial: 8250: add option to disable registration of legacy ISA ports

From: Maarten Brock
Date: Thu Feb 18 2021 - 08:52:55 EST


On 2021-01-31 14:18, Måns Rullgård wrote:
What userspace visable change will be caused by this?

There won't be /dev/ttyS devices for ports that don't exist.

Oh yes, please!

That would mean I can create ttyS2 and upward while keeping ttyPS0 and ttyPS1 (which invaded the serial<N> alias namespace) at the lower numbers.

Will ports get renumbered?

Not if they had predictable numbers to begin with.

It is hard to make predictable numbers with the backward operating serial<N> aliases in the device tree. It makes relations in the wrong direction.

If a system has two ttyPS<N> uarts (xilinx_uartps) and needs them at ttyPS0 and ttyPS1 (or at least <=ttyPS9, due to another bug in start_getty) and 10 ttyS<N> (8250) you can configure the kernel for 10 8250 devices and give 8 of them the predictable ttyS2 to ttyS9. The last two will get the remaining ttyS0 and ttyS1. You cannot assign them their number, because the serial0 and serial1 alias are required for the ttyPS0 and ttyPS1.

However with this option it would be possible to configure for 12 8250 devices and not use nor see ttyS0 and ttyS1.

The best option would of course be to not even instantiate kernel drivers for non-existing devices.

Maarten