tlug: SCSI and Ethernet sharing same IRQ

["Robert J. Bickel" <rob@example.com>]

I posted a question about this sometime ago and got some
help from tlug guys.  I finally solved my problem and I think
the solution was not so evident, so I thought I would share what
I learned.

1.  I learned that with PCI you can have any number of devices
    sharing the same IRQ including an ethernet card and a scsi
    card (my case).  Also my video adapter also uses the same
    IRQ.  

2.  If you want this to work correctly your OS must support 
    the IRQ sharing.  Luckily most recent linuxes do.  I 
    understand any 2.0.x or 2.1.x should support IRQ sharing.

3.  If you are using the aic7xxx driver for the Adaptec SCSI card
    then it will not allow you to share the IRQ, unless you
    make one simple change.  I think this problem is not rare
    since Adaptec SCSI is pretty common.  Anyway, you need
    to delete an instance of the flag SA_INTERRUPT.  This
    flag occurs once in aic7xxx.c in as part of an if statement.
    Delete only SA_INTERRUPT.  Recompile your kernel and
    you too will be able share your IRQ with an ethernet card
    and your Adaptec SCSI.
     (I am using linux kernel 2.0.30, if you use another kernel
     your case may be different - in fact the problem may be
     fixed in 2.1.x or 2.0.31 I am not sure).

Finally, I don't want to take credit for this bit of device driver
programming.  I found the answer using deja news.  It took a while
to find the right answer.  There were a lot of people with my same
problem, but a lot of the responses they got simply were not 
correct.  There are a lot of people who think that the IRQ sharing
was the problem (I was one until recently).  IRQ sharing is okay.

Rob

****************************************************************
Robert Bickel, Lecturer
Tokyo University of Agriculture and Technology
2-24-16 Nakacho, Koganei-shi, Tokyo 184
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e-mail: bickel@example.com
http://kichijoji.mech.tuat.ac.jp/~rob/robw.html

In Japanese
東京農纔瘢韭絎竢踪大学、講師
〒184東京都小金井市中町2ー14ー16
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