Subject: Re: No IDE-DMA after sup today ("no driver support")...
To: Charles M. Hannum <>
From: Manuel Bouyer <>
List: current-users
Date: 10/21/1998 09:11:59
On Oct 21, Charles M. Hannum wrote
> A few days ago, Manuel changed the pciide driver to not enable DMA
> unless it recognizes the specific product ID of the chip.  The product
> ID for you IDE chip is not listed in the driver.  Ergo, DMA is not
> being enabled.
> I tend to think this is kind of a lose.  A device claiming to be a PCI
> IDE controller will in general properly support the spec; ones that do
> not are the exception, and should be treated as such.

DMA operation is in specs, but the DMA modes setups are not. So each
PCI IDE vendor do it his own way, and a machine where the controllers
and drive DMA modes don't agree will hang solid at the first disk
access. No interrupts, no timeout callback possibe: it hangs. This prevent
any king of "try DMA and fall back to PIO if it fails" algorithm, as
I wanted to do it the first time.

This was with a PIIX4. Maybe some other controllers have a more fair
behavior. But I think it's better to say "your disk is used in PIO
mode because the pciide driver doesn't support your controller" than
"your machine hang when you try to install NetBSD on it because
the pciide driver doesn't support your controller".

Manuel Bouyer, LIP6, Universite Paris VI.