On Mon, Nov 10, 2014 at 1:50 PM, Kevin Cernekee <cernekee@xxxxxxxxx> wrote: > On Mon, Nov 10, 2014 at 11:22 AM, Rob Herring <robh@xxxxxxxxxx> wrote: >>>> 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? >> >> No, but I think you can do dynamic minor numbers. I seem to recall >> this coming up with the Samsung UARTs a while back. > > The other variations I've seen in the tree are: > > nwpserial: ttySQ, major 4 minor 68 (not 64) > > sunhv, sunsab, sunsu, sunzilog: set uart_driver->major to 4 but let > uart_driver->minor default to 0 > > SERIAL_ATMEL_TTYAT: compile-time selectable between ttySn (4/64) and > ttyATn (204/154). txx9 does something similar using > SERIAL_TXX9_STDSERIAL. > > A whole bunch of other SoC serial drivers use major 204 and a custom > name like "ttyAL". Some of these show up in > Documentation/devices.txt; others don't. ~3 drivers use 204/64 from > the middle of the Altix assigned range. > > What is the current best practice for new drivers? I think it would be using dynamic numbering, but would be good to have others weigh in here. It looks like a dynamic major would solve your problem. See tty_register_driver. Also, there was a patch to make this the fallback behavior instead of an error[1], but it was never merged (and it's not clear why). This was the Samsung related change I was remembering. Rob [1] http://lists.linaro.org/pipermail/linaro-kernel/2014-January/010383.html
