[PATCH] Stop pmac_zilog from abusing 8250's device numbers.
rmk+lkml at arm.linux.org.uk
Wed Apr 4 18:51:59 EST 2007
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
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
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
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