Hello, all.

Broken MWDMA on pata_ali has caused a number of bug reports.  I've been
trying to fix it for some time now && finally got a machine with
pata_ali and non-working MWDMA2 ATAPI device on my desk a few weeks ago.
 Testing confirms what users have been reporting - MWDMA2 works fine
with the IDE alim15x3 driver while any DMA data transfer on pata_ali
times out.

At first I thought this was simple timing programming error, but no.
pata_ali's mode programming wasn't wrong although it was different in
how it programs empty slots.  Even after making pata_ali to program the
controller exactly the same as alim15x3 (identical lspci -xxx results),
MWDMA didn't work. (attached)

I wondered whether the device was configured differently, so compared
hdparm --Istdout results.  They were identical too. (attached)

I walked through IDE and libata codes and found some differences in the
order registers are accessed and which values are written (e.g. libata
never turns on device 0/1 DMA capable bits in BMDMA status register
while IDE does).  I made them access the registers in the same order and
write the same values.  Still no go.

Then, I made libata probing sequence very close to IDE such that no
reset is performed and NIEN isn't tempered with.  No go.

I thought maybe the drive should just be blacklisted.  I took the laptop
apart, took out the DVD combo drive to ICH7 ata_piix.  It works just fine.

So, I'm out of ideas at this point.  Any suggestions?  Ideas?

Thanks.

-- 
tejun