linux-kernel - Re: Disabling DMA with ICH10?

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Message-ID: <20090929180555.3c4a7259@lxorguk.ukuu.org.uk>
Date:	Tue, 29 Sep 2009 18:05:55 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Krzysztof Halasa <khc@...waw.pl>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	"Lennart Baruschka" <FunFlyer@....net>,
	linux-kernel@...r.kernel.org
Subject: Re: Disabling DMA with ICH10?

On Tue, 29 Sep 2009 14:29:27 +0200
Krzysztof Halasa <khc@...waw.pl> wrote:

> Arjan van de Ven <arjan@...radead.org> writes:
> 
> > a single PIO instruction will NOT be interrupted by an interrupt.
> > And can easily take several microseconds (remember: 8Mhz bus
> > emulation)
> 
> Not that long, there is no emulation there (except for port #80 (hex?)
> and similar). Normal 33 MHz access.

ATA accesses go across the cable and while some of them are snooped,
cached and other magic is done there are cases it turns into a
transaction back and forth with the drive - that *is* slow. PIO 0 in fact
is ISA speed
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