Re: [PARPORT] lp

Andrea Arcangeli (
Wed, 1 Apr 1998 16:05:49 +0200 (CEST)

On Wed, 1 Apr 1998, Tim Waugh wrote:

>The behaviour of the printer driver has changed between 2.0 and 2.1 in
>that it now defaults to being interrupt-driven if parport can find out the
>IRQ to use. It's been suggested that this is a bad thing, since it can
>cause clashes that previously would have caused no harm.

If the parport lowlevel driver will autodetect the right irq I don' t see
how can it cause an harm. I don' t see the problem how lp specific but
instead as parport_lowlevel specific. If lp will cause an harm every other
pardevice that will use interrupt on the same parport will do the same.

>So, my plan is to utilise tunelp. lp defaults to polling until given a

I don' t like lp defaults to polling. If the parport_lowlevel driver will
no detect the irq (or it is not forced to use one) lp run polled just now.

>non-zero IRQ by tunelp -i. Then it uses whatever IRQ parport found, or
>returns -EINVAL if there was none. (Currently, tunelp -i will always
>get -EINVAL.)

Updating tunelp to work with the current lp is a good thing to do. We
could use -i and +i to disable/enable lp interrupt printing. BTW, In the
lp code we had to touch only the LP_POLLING() macro to take care of
another flag.

>It would also be good to have a module parameter to enable
>interrupt-driven operation from the outset. A kernel parameter would be
>good too, but I can't think of a good syntax for it (anyone?).

It would be nice but I don' t think it' s really needed. If somebody will
need to change the default settings can add:

post-install lp tunelp /dev/lp? -/+i

to /etc/conf.modules if lp is a module, or can run it at boot time (maybe
we could tell this in the parport docs when tunelp will work).

Andrea[s] Arcangeli

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This archive was generated by hypermail 2.0b3 on Wed 30 Dec 1998 - 10:17:34 EST