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SubjectRe: [PATCH] PnP Changes for 2.5.72
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+On 172, 06 21, 2003 at 05:53:59 +0000, Thorsten Kranzkowski wrote:
> On Fri, Jun 20, 2003 at 02:00:14PM -0400, Bill Davidsen wrote:
> > On Fri, 20 Jun 2003, Andrey Panin wrote:
> > > On 171, 06 20, 2003 at 06:55:47AM +0100, Russell King wrote:
> > > > The problem is one of a lack of historical information on why it was
> > > > added. The driver itself allows serial ports to share interrupts between
> > > > themselves. Maybe tytso knows why the "Rockwell 56K ACF II Fax+Data+Voice
> > > > Modem" is unable to share IRQs?
> > >
> > > It was me who added this crappy quirk.
> > >
> > > My ELine modem which identified itself "Rockwell 56K ACF II Fax+Data+Voice Modem"
> > > was going mad when its IRQ was shared with any device. So I decided to add this
> > > quirk.
> > >
> > > Personally I think that ISA IRQ sharing should be absolutely last resort technic,
> > > because ISA bus was never designed to support IRQ sharing sanely. If you have to
> > > enable ISA PnP device and do not have enough IRQ, you must print BIG FAT WARNING
> > > before doing this. May be kernel config options must be added for brave guys
> > > wanting to use ISA IRQ sharing.
>
> Problem is, 'unprepared' ISA cards are electrically unable to share interrupts
> (like in: an interrupting card cant't drive the interrupt line high while at
> the same time another one actively drives it at a low level). You _can_ make
> things work when you replace the IRQ-selection-jumper on all sharing devices
> with a diode and add a pull down resistor. BTDT - works sufficiently well.

Problem is that almost all all ISA cards fall into 'unprepared' category,
unable to share interrupts with another card. ISA IRQ sharing allways was the
risky bussiness, depending on electrical characteristics of both IRQ sharing
devices.

> > But dumb multiport boards support sharing just fine:
>
> Yes, they usually contain the necessary sharing circuity onboard. But you
> can't share them with other instances of the same or other cards unless you
> make the modifications above.
>
> Unfortunately on-board serial ports seldom have IRQ-jumpers - which makes them
> practically not shareable at all.

It's exactly my point beyond the ugly quirk which disables ISA IRQ sharing.

>
> And for PNP devices, well they also don't have jumpers. It is possible
> to find the necessary wires on the pcb though ..... ;-)

Reverse enginerring of the PCB layout is not acceptable for allmost all users
of ISA PnP boards :)

--
Andrey Panin | Linux and UNIX system administrator
pazke@donpac.ru | PGP key: wwwkeys.pgp.net[unhandled content-type:application/pgp-signature]
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