On Tue, 8 Sep 2009, Alan Cox wrote: > > I've got a situation where a drive claims to be capable of supporting > > UDMA/100, but it's in a noisy environment and gets lots of errors at > > that speed. I'd like to limit it to UDMA/66 or even UDMA/33. > > That should never occur with a proper cable and I would be concerned the > fault might be something more problematic such as speed misconfiguration > or an incompatibility. Which driver is in use ? The cable indeed is likely to be at fault. The same drive worked okay at the higher speed with a different cable (which unfortunately is unavailable for use in the final deployment). This is using the old IDE driver. Here's an extract from the log, with ide-core.ignore_cable=0 specified on the command line: Linux version 2.6.27-gentoo-r10 (root@raise) (gcc version 4.1.2 (Gentoo 4.1.2 p1.0.2)) #1 SMP PREEMPT Tue Apr 21 15:06:03 UTC 2009 ... Uniform Multi-Platform E-IDE driver piix 0000:00:1f.1: IDE controller (0x8086:0x24cb rev 0x02) pci 0000:00:1f.1: PCI INT A -> GSI 18 (level, low) -> IRQ 18 piix 0000:00:1f.1: IDE port disabled piix 0000:00:1f.1: not 100% native mode: will probe irqs later ide: ignoring cable detection for ide0 ide0: BM-DMA at 0xf000-0xf007 Probing IDE interface ide0... hda: STEC MACH-8 SSD, ATA DISK drive hda: host max PIO4 wanted PIO255(auto-tune) selected PIO4 hda: UDMA/100 mode selected ide0 at 0x1f0-0x1f7,0x3f6 on irq 14 ide_generic: please use "probe_mask=0x3f" module parameter for probing all legacy ISA IDE ports ide_generic: I/O resource 0x1F0-0x1F7 not free. ide_generic: I/O resource 0x170-0x177 not free. hda: max request size: 512KiB hda: 60789456 sectors (31124 MB), CHS=16383/255/63 hda: cache flushes not supported hda: hda1 hda2 hda3 ... hda: dma_intr: status=0x51 { DriveReady SeekComplete Error } hda: dma_intr: error=0xc4 { DriveStatusError BadCRC UncorrectableError }, LBAsect=14823116, sector=14823116 ide: failed opcode was: unknown hda: dma_intr: status=0x51 { DriveReady SeekComplete Error } hda: dma_intr: error=0xc4 { DriveStatusError BadCRC UncorrectableError }, LBAsect=15133492, sector=15133492 ide: failed opcode was: unknown hda: dma_intr: status=0x51 { DriveReady SeekComplete Error } hda: dma_intr: error=0xc4 { DriveStatusError BadCRC UncorrectableError }, LBAsect=9478100, sector=9478100 ide: failed opcode was: unknown Etc.; you get the idea... > > The hdparm command should be able to do this but I can't run it until > > the system has booted, by which time a bunch of CRC and possibly other > > errors have already occurred. Ideally it should be possible to limit > > Only the data transfers are CRC protected and at high speed, but noise at > low speed would be a real concern as the commands are sent low speed but > without protection on PATA devices - so a bit flip can send a DMA to the > wrong sector. > > > the speed starting as early as device detection, but I can't find any > > way to do it. Is there support for such a thing or will I have to hack > > it in? > > You can disallow DMA but not clip DMA to UDMA33 with the old driver. You > could disallow DMA at boot and reallow it with a speed set by hdparm in > your boot scripts... On Tue, 8 Sep 2009, Frederik Deweerdt wrote: > Does passing ide=nodma at bootime, and then having init set the DMA at > the right speed, would work? I'll recommend trying that out. Thanks to both of you for the advice. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html