On Mon, Nov 10, 2014 at 6:25 AM, Rob Herring <robh@xxxxxxxxxx> wrote: > On Sun, Nov 9, 2014 at 2:55 AM, Kevin Cernekee <cernekee@xxxxxxxxx> wrote: >> By default, bcm63xx_uart.c uses the standard 8250 device naming and >> major/minor numbers. There are at least two situations where this could >> be a problem: >> >> 1) Multiplatform kernels that need to support some chips that have 8250 >> UARTs and other chips that have bcm63xx UARTs. >> >> 2) Some older chips like BCM7125 have a mix of both UART types. >> >> Add a new Kconfig option to tell the driver whether to register itself >> as ttyS or ttyBCM. By default it will retain the existing "ttyS" >> behavior to avoid surprises. > > While I understand the desire to have stable names, this is the > opposite direction we want to go. Per platform tty names complicates > having a generic userspace. It is not so bad since most ARM platforms > use ttyS or ttyAMA, but just think what the kernel and userspace side > would look like if every single platform did this. We can't change > everything to ttyS because the other names are already an ABI. > > This can be solved with a udev rule to create sym links. Is it safe to register two console drivers named "ttyS" with the same major/minor numbers? Maybe there is a trick to making them coexist? What I found is that everything worked fine on a system with bcm63xx_uart hardware until I enabled the 8250 driver in .config. At that point the drivers clashed and I had no serial output post-bootconsole. It didn't even get to userland before it failed. There are no DT entries mentioning 8250; the mere presence of the 8250 driver killed my console. If this behavior is unexpected I can keep digging to find out what went wrong. > Or if you > just need to know which dev node is h/w uart X, you can get that from > sysfs. Right - I use busybox cttyhack in the init scripts to figure out the console name, so the same rootfs image can be used for both ttyS0 and ttyBCM0: # Put a shell on the serial port ::respawn:/bin/cttyhack /bin/sh -l
