I run into hard system hangs with my promise controller (kernel:
2.4.19-pre4-ac3)

Background:

* Harddisk with bad sectors.
* reading from one of the bad sectors usually causes error messages, but
sooner or later the kernel falls back from UDMA to pio.
* obviously pio doesn't work either, and ide_error is called.
* the fallback works if the harddisk is connected to a via VT82C686
south bridge.
* the fallback causes a total system hang if the drive is connected to
the promise controller.
* it hangs on the "rep;insw;" instruction in ata_input_data(), called by
try_to_flush_leftover_data().

Before someone replies that I should not try to read bad sectors: The
harddisk was used in a headless server, and I did not expect that sector
errors cause system crashes. And the crash defeats the purpose of
software raid1.

Any idea where I should continue to search? It seems that the pdc20269
controller doesn't handle the error fallback to pio. If I boot with
"ide=nodma", then pio works.

I've attached lspci and dmesg. If you have further questions, please
ask. I have a test setup with kdb.

--
    Manfred