On Tue 2024-06-11 12:56:54, Tony Lindgren wrote: > On Tue, Jun 11, 2024 at 10:17:11AM +0200, Petr Mladek wrote: > > On Thu 2024-06-06 14:41:46, Tony Lindgren wrote: > > > Recent changes to allow using DEVNAME:0.0 style console names caused a > > > regression to the kernel command line handling for the console options. > > > > Sigh, I have missed that it has already ended in the mainline via > > the tty tree :-/ > > > > Honestly, I would prefer to revert it and implement it a clean way. > > I see a lot of existing and possible problems: > > Naturally no objection from me for reverting if there are issues that are > unfixable from the printk point of view. I'll update the fix along the > lines you're suggesting below though, let's see if that's enough for the > -rc cycle. OK, let's see how the updated fix looks like. > > 1. Where and how is DEVNAME:0.0 defined? > > > > The only documentation seems to be in > > Documentation/admin-guide/kernel-parameters.txt for the console= > > parameter: > > > > <paste> > > <DEVNAME>:<n>.<n>[,options] > > Use the specified serial port on the serial core bus. > > The addressing uses DEVNAME of the physical serial port > > device, followed by the serial core controller instance, > > and the serial port instance. The options are the same > > as documented for the ttyS addressing above. > > > > The mapping of the serial ports to the tty instances > > can be viewed with: > > > > $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* > > /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 > > > > In the above example, the console can be addressed with > > console=00:04:0.0. Note that a console addressed this > > way will only get added when the related device driver > > is ready. The use of an earlycon parameter in addition to > > the console may be desired for console output early on. > > </paste> > > > > This seems to be a brand new bus. > > > > Is it stable? > > Is it documented in Documentation/ABI/stable/? > > I think the DEVNAME originates from udev to be used for various rules. Yes > it should be documented somewhere though. I'd say it's stable as it's been > in use for years :) > > > It seems that the feature will cover "only" serial consoles. > > But DEVNAME is a generic name. It might make more sense to > > call it "SERIAL_BASE_DEVNAME" or "SERIAL_DEVNAME" or "SBASE_DEVNAME" or so. > > > > Anyway, console= is an interface with the user space. We will need to > > maintain the backward compatibility "forever". > > > > => we should think twice about the interface !!! > > I think we want to keep it generic with DEVNAME, I don't see why we'd want > make it serial console specific, at least in the code. For the documentation, > I think the kernel parameters example is clear on the serial port usage? OK, let's keep the DEVNAME in both the code and documentation, > > 3. The delimiter between "DEVNAME" and X.Y numbers is ":". > > But ":" is also part of the sample DEVNAME "00:00" > > > > Is it a good idea? > > > > Is the current naming scheme a well known historic one > > or something invented for the new bus? > > PCI and USB use a ":" already for the device naming. Also a "-" can be used > by the device names, many platform devices do that. I don't think we can > pick any better limiter here, at least out of the ":", "-" and "." options. OK, it seems that ':' is the best choice. And thanks for explaining the other details. Everything makes more sense now. Best Regards, Petr
