2.4.x swim3 performance problem on PM4400 identified

[mikpe at csd.uu.se]

Paul Mackerras writes:
 > Mikael Pettersson writes:
 >
 > > With 2.4 kernels, writes to floppy are about a factor of 10 slower
 > > on my PowerMac 4400 than they are with 2.2 kernels.
 > >
 > > The cause for this is a poll-loop in swim3.c which doesn't exist
 > > in the 2.2 version. The patch below reverts that change, and
 > > restores floppy write performance to 2.2 levels. I've built many
 > > boot floppies with this modified driver w/o any problems.
 >
 > This finally prodded me to look at the mach driver.  I've hacked the
 > linux swim3 driver to do things in a more similar fashion to what the
 > mach driver does.  It now seems to not get stuck on the dreaded 04
 > error and generally seems a lot more robust.  Try this patch and let
 > me know how it goes.

I finally got around to testing your updates to swim3.c. I haven't
observed any problems with it, and it solved my slow-writes problem.
Great work -- thanks.

There are two compile warnings on unused variables 'swim3_buf' and
'max_wait_inactive' that your update introduces. Did you intend
to use them or what?

/Mikael

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