Messages in this thread | | | Date | Sun, 26 Jul 1998 20:25:48 +0400 (IDT) | From | Gadi Oxman <> | Subject | Re: 2.1.111: IDE DMA disabled? |
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On Sat, 25 Jul 1998, Linus Torvalds wrote:
> Which implies that at _least_ we need to disable DMA automatically if it's > one of those chipsets. > > Personally, I never understood why DMA was enabled by default anyway. As > far as I can tell the only sane thing is to have it always disabled by > default, and enable it with hdparm. > > Linus
It is not enabled by default unconditionally; we currently enable DMA only for drives which support DMA mode 2 and above (introduced along with PIO mode 4), which filters out old (and possibly buggy) DMA implementations.
We might want to switch to a stricter rule, but the above rule was used by the kernel ide-dma driver from the very begining, around 1.3.50 or so, and through all that time we have not received many reports about DMA-specific data corruption.
If the corruption in this case will indeed be fixed by replacing the IDE cable or by lowering the chipset timing, I believe that we are likely to see data corruption eventually, even without DMA, and the real fix is to use a shorter IDE cable or to lower the timings in the BIOS -- we can work around chipset bugs and black-list specific drives if there is enough evidence which shows such bugs, but I believe that there is really not much to be done in software regarding a bad IDE cable; even in PIO mode, we have seen data corruption with high PIO modes and with long IDE cables in the past.
Gadi
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