* Andy Shevchenko <andriy.shevchenko@xxxxxxxxx> [230719 13:59]: > On Wed, Jul 19, 2023 at 08:43:21AM +0300, Tony Lindgren wrote: > > * Andy Shevchenko <andriy.shevchenko@xxxxxxxxx> [230719 05:34]: > > > On Wed, Jul 19, 2023 at 08:16:11AM +0300, Tony Lindgren wrote: > > > > Let's allow the userspace to find out the tty name for a serial core > > > > controller id if a tty exists. This can be done with: > > > > > > > > $ grep DEVNAME /sys/bus/serial-base/devices/port*/tty/uevent > > > > /sys/bus/serial-base/devices/port.00:04.0/tty/uevent:DEVNAME=ttyS0 > > > > /sys/bus/serial-base/devices/port.serial8250.1/tty/uevent:DEVNAME=ttyS1 > > > > /sys/bus/serial-base/devices/port.serial8250.2/tty/uevent:DEVNAME=ttyS2 > > > > /sys/bus/serial-base/devices/port.serial8250.3/tty/uevent:DEVNAME=ttyS3 > > > > > > What part is the controller ID here? > > > > Oh looks like controller id it's missing in the name, I'll send a fix > > for that. > > > > > We also have something in procfs (I don't remember what info exactly is there). > > > > Do you mean /proc/devices? > > Something tty specific, /proc/tty/, but I had a look and it seems for another > stuff. OK > > > > And with this, we can add /dev/serial/by-id symlinks to the serial port > > > > device instances so we can start using serial core port addressing in > > > > addition to the legacy ttyS naming. > > > > > > > > The naming we can use is dev_name:0.0 where 0.0 are the serial core > > > > controller id and port id, so for the ttyS0 example above the naming > > > > would be 00:04.0:0.0. > > > > > > This is interesting idea. But any hint why it can be useful? > > > > If you have lots of serial ports and we are stuck with adding aliases > > for the ports in the dts files where the ttyS naming and ordering does > > not really help or may not necessarily make sense if the ports are on > > different buses or domains. With CONFIG_SERIAL_8250_RUNTIME_UARTS=4, > > the ttyS naming is only needed for the legacy ports really. > > I see. Does it fix the long standing issue with ttyS enumeration (on x86 > at least) when depending on the presence of the legacy ports the HSUART > (high speed) can preempt the legacy placeholders (ttyS0..ttyS3)? > > To me sounds like it may very well do fix it and I would be glad to see that > in the commit message (as selling point) and in documentation. It won't affect how ttyS0..ttyS3 get assigned, but it helps finding your HSUART instance with DEVNAME:0.0 style addressing. So you don't need to care what ttyS number the port has. If you have such a test case maybe give it a try. Regards, Tony
