Re: [PATCH] Serialize CMD643 and CMD646 to fix a hardware bug with SSD

[Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>]

On Wednesday 21 October 2009 20:55:28 Mikulas Patocka wrote:
> Hi
> 
> This patch fixes a data corruption when SSD is connected to Ultra 5.
> 
> Mikulas
> 
> --
> 
> Serialize CMD643 and CMD646 to fix a hardware bug with SSD
> 
> CMD646 corrupts data on concurrent transfers on both channels when IDE SSD is
> connected to one of the channels.
> 
> Setup that demonstrates this hardware bug: Ultra 5, onboard CMD646, rev 3.
> /dev/hda is 8GB Seagate ST38410A in MWDMA2
> /dev/hdd is 32GB SSD SiliconHardDisk in MWDMA2
> 
> - When reading /dev/hdd (for example with dd or fsck), reads from /dev/hda
>   are corrupted, there are twiddled single bits 1->0 and some full 32-bit
>   words corrupted, sometimes commands fail (which switches /dev/hda to
>   PIO mode but the corruptions happen even in PIO).
> - Reads from /dev/hdd don't seem to be corrupted (i.e. fsck passes fine).
> - When I connected normal rotating harddisk to /dev/hdd, there was no
>   corruption, so the corruption is something specific to SSD.
> - I tried the same setup on a PCI card with CMD649 and saw no corruption.
> 
> This patch serializes the operation for CMD646 and 643 (I didn't test
> CMD643 but it may have the same hw bug too because it's earlier design).
> CMD649 is good. I don't know anything about CMD 648.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Seems like SSD (simply by being faster) triggers some race condition that
hardware has tolerated in the past and since we used to always serialize
operation for CMD646 before:

commit e01698aed04811b9a9c4f8d54b73cb182757063d           
Author: David S. Miller <davem@davemloft.net>             
Date:   Sun Jun 21 22:48:03 2009 -0700

    ide cmd64x: Remove serialize setting.

it went undetected until now..