Date: Thu, 16 Mar 2000 09:51:18 -0800
From: Jurgen Botz <jurgen@xxxxxxxx>
Richard Gooch wrote:
> In drivers/char/serial.c:register_serial() there are calls which
> create devfs entries. So the low-level serial driver should call
> register_serial() and everything should be fine. It certainly works
> for PCMCIA serial cards. Insert the card and the devfs entry magically
> appears.
The problem is that ISA multiport serial cards don't appear to be
detected by the kernel at all and register_serial never gets called.
To use the ports you set the IO base and IRQ with setserial which
sets them in the driver with ioctls on the device. This bypasses
register_serial in the driver, too, so even if I create /dev/ttyS2
and then do the setserial thing, /dev/tts/2 still doesn't appear
(but /dev/ttyS2 then works fine). Not that that would make a
difference for devfs, of course.
Right. There are actually two parts to this problem. The first is that
when setserial calls TIOCSSERIAL to change the uart from "none" to
"non-none" and vice versa, tty_register_devfs() and
tty_unregister_devfs() needs to be called. I can fix this in the serial
driver fairly easily, and this will take care of the problem which you
reported.
The second problem is how do you actually get setserial to set the port,
irq, and uart settings using only devfs in the first place. The issue
here is that you can't autodetect ISA multiport serial cards, at least
not those cards that don't have PNP support. The port and irq settings
either have to manually configured such as is the case for COM 1/2/3/4,
or the user has to manually set them using the setserial command.
But, in a devfs only world, the device file doesn't appear until the
port is configured, but setserial needs the device file in order to
configure the port. There's no real way around this....
That may not be worth the trouble to provide automatic devfs
support for the diminishing number of non-PNP ISA multiport
boards out there. Since I currently have to run an rc script
to configure the ports anyway, I might as well create the device
files there with mknod.
Perhaps, but this isn't very satisfying; it's certainly very awkward for
users, and for people who were accustomed to things Just Working (tm) in
Linux 2.2, it's really, really, really ugly to tell them that they have
to manually mknod the device in devfs. However, short of telling them
(a) don't use devfs, or (b) hacking setserial to automatically do the
mknod if /dev/ttyS* is passed in and /dev/ttyS* doesn't exist. Both
aren't pretty solutions, though.
What makes this worse is that I've been encouraging people to use rc
scripts for configuring ISA multiport cards, since there are so many of
them and using compiled in, hard-coded configuration parameters is
evil. The /devfs model doesn't seem to allow this terribly easily,
unfortunately.
I suppose we could shovel all of this dirt under the devfsd rug, and
make devfsd responsible for parsing some new serial configuration file
which then does the mknod and TIOCSERIAL ioctl. But that's not that
great of a solution either.
I'll need to think about this one some more. I'm not particularly
happy with any of these solutions. Richard, what do you think?
- Ted
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