kern/8875: Patch to allow DMA IDE with generic chipset + UDMA drives (fwd)

[Nick Hibma]

The following reply was made to PR kern/8875; it has been noted by GNATS.

From: Nick Hibma <nick....@jrc.it>
To: freebsd-gn...@freebsd.org
Cc:
Subject: Re: kern/8875: Patch to allow DMA IDE with generic chipset + UDMA drives (fwd)
Date: Sat, 24 Jul 1999 20:48:48 +0200 (MET DST)

---------- Forwarded message ----------
Date: Sun, 25 Jul 1999 04:36:49 +1000
From: Bruce Evans <b...@zeta.org.au>
To: n_h...@FreeBSD.ORG
Subject: Re: kern/8875: Patch to allow DMA IDE with generic chipset + UDMA drives

>Synopsis: Patch to allow DMA IDE with generic chipset + UDMA drives
>
>State-Changed-From-To: open->analyzed
>State-Changed-By: n_hibma
>State-Changed-When: Sat Jul 24 04:21:24 PDT 1999
>State-Changed-Why:
>It looks like an additional feature that is no longer necessary.
>If I remeber correcctly support for Ali and Sis has been added).

An unifdefed version of it was committed in rev.1.23, but should
not have been. It was a quick fix for the author's Ali motherboard
or BIOS but it is obviously wrong in general since it bogotifies the
comment preceding it (the point of the "generic" support is to assume
that everything is already set up correctly; any hardware programming
risks disturbing the setup). It broke generic support on at least one
of grog's systems (SiS IIRC). rev.1.23 also added Ali support, so the
patch in the PR was certainly unnecessary for Ali. The SiS breakage
was fixed a little later by adding proper SiS support.

The ata driver does the same things as the patch. It's not clear that it
helps there. It may harm by reprogramming the drive from UDMA2 to WDMA2.
I think something like this happens on one of my systems, but it doesn't
harm throughput or overhead. I only have PIIX1, VIA2 and PIIX4 to test.

Bruce

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