linux-kernel - Re: How to Switch DMA off for only one Harddisk at Kernelboot

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Message-ID: <20071218000405.19d2c706@the-village.bc.nu>
Date:	Tue, 18 Dec 2007 00:04:05 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
Cc:	Oliver Joa <oliver@...-a.de>, linux-kernel@...r.kernel.org
Subject: Re: How to Switch DMA off for only one Harddisk at Kernelboot

> Isn't it more a matter of having a CF card that does do DMA and a
> controller that does DMA, but a CF to IDE adapter that does not do DMA?

Usually yes. 

If your CF card doesn't support DMA it will advertise PIO modes only and
all will be well. If your card can do DMA it will advertise DMA modes
regardless of whether your CF adapter has the needed pins wired.

For UDMA it is even worse. Most CF adapters that can do DMA do not
provide sufficient signal quality for UDMA. In addition if you hang them
off a normal UDMA 2 device cable you are miles out of spec and some cards
work some of the time.

Alan
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