Re: [PATCH] Stop pmac_zilog from abusing 8250's device numbers.

Geert Uytterhoeven
2007-04-04T09:48:16Z

On Wed, 4 Apr 2007, Russell King wrote:
> On Tue, Apr 03, 2007 at 04:09:08PM -0700, Brad Boyer wrote:
> > The availability of the specific chip in question is a red herring in
> > my opinion. I do understand that 8250 compatible chips are very common
> > and are the most likely serial chips to be used with Linux. However, I
> > will point out that the define is TTY_MAJOR, not 8250_MAJOR. It seems
> > to me that whoever named it was thinking in more generic terms.
>
> You're reading too much into the name. It's historical, and the reason
> can still be seen in LANANA:
>
> 4 char TTY devices
> 0 = /dev/tty0 Current virtual console
>
> 1 = /dev/tty1 First virtual console
> ...
> 63 = /dev/tty63 63rd virtual console
> 64 = /dev/ttyS0 First UART serial port
> ...
> 255 = /dev/ttyS191 192nd UART serial port
>
> UART serial ports refer to 8250/16450/16550 series devices.
>
> When the drivers/char/serial.c driver was written, it was in the very
> early days of Linux. I'd guess that the major/minor numbers were similar
> to Minix, thereby allowing a minixfs to be used as the initial filesystem
> type.
>
> Anyway, as you can see, defining chardev major 4 to be "8250_MAJOR" would
> also be a misnomer because it's used for the virtual consoles, and it's
> _that_ use for which it (probably) was called TTY_MAJOR.
>
> (Note that in the very early days, this major also got used for PTY
> devices. Since then they've moved to major 2/3 and then we got Unix98
> PTY support.)

Oh, and I always thought PTYs were moved to free up more minors for our
zillions of serial ports...

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds