Re: [PATCH 2/2] tty: serial: bcm63xx: Allow device nodes to be renamed to /dev/ttyBCM*

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Nov 10, 2014 at 07:05:14AM -0800, Kevin Cernekee wrote:
> On Mon, Nov 10, 2014 at 6:25 AM, Rob Herring <robh@kernel.org> wrote:
> > On Sun, Nov 9, 2014 at 2:55 AM, Kevin Cernekee <cernekee@gmail.com> 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?

Not at all, think about what you are asking for here.

Is the kernel allowed to register two block devices with the same
major/minor numbers?

greg k-h