DMA disabled by default for optical drives - why?

James Gray james at grayonline.id.au
Wed Dec 21 22:58:17 UTC 2005


On Tue, 20 Dec 2005 21:23, Robert Entner wrote:
> On Tuesday 20 December 2005 07:25, James Gray wrote:
> > On Tuesday 20 December 2005 07:39, Jason Smith wrote:
> > > After I have installed Ubuntu 5.10 I din't manage to write not even
> > > one DVD, because DMA was not enabled. Not to mention
> > > the high CPU usage when I was accessing my optical drive.
> > >
> > > Luckily Nero warned me about the DMA misconfiguration, I corected the
> > > problem
> > > and now everything works fine. I think DMA should be enabled by
> > > default.
> >
> > All well-and-good, but what if the Ubuntu installer loads the
> > ide-generic driver before your chipset-specific IDE driver resulting in
> > a situation that setting DMA on any drive causes a kernel panic?  Not
> > Ubuntu's fault mind you - it was a known gotcha with early Asus K8VSE
> > motherboard BIOS'es..
> >
> > So enable DMA by default and possibly panic the kernel if the BIOS is a
> > little screwy, or play safe?  Personally, I'd rather have a machine
> > that boots (even at sub-optimal speed) so I can fix the problem over a
> > system that panics before it even reaches run level 1. :)  It's not
> > just old hardware that can e flakey with DMA enabled by deafult -
> > unfortunately.
>
> How does Windows solve this problem?

Simple.  Asus wrote a driver specifically for Windows - I couldn't enable 
DMA until the driver was installed in Windows either.  Problem solved.  In 
the open source world, non-Asus developers had to string together a driver 
from a mix of incomplete manufacturer specs and reverse engineering.

I'm not at all surprised the Ubuntu installer didn't get it exactly right, 
but before I started forcing things (like enabling DMA) it *was* 
stable....just slower than it could be.  After fixing the driver load 
order, DMA works like a charm!

Don't /blame/ Linux for the lack of support for a particular piece of 
hardware; blame the manufacturer for not supporting Linux.  How do you 
think Windows supports all the hardware?  M$ certainly didn't write a 
driver themselves - they rely on manufacturers supporting their OS.

Support the companies that support open source!

Cheers,

James
-- 
Real computer scientists admire ADA for its overwhelming aesthetic
value but they find it difficult to actually program in it, as it is
much too large to implement.  Most computer scientists don't notice
this because they are still arguing over what else to add to ADA.
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