linux-kernel - Re: [PATCH] Fix DMA on Dreamcast

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Date:	Sat, 21 Jul 2007 16:13:19 +0200
From:	"Peter Bortas" <bortas@...il.com>
To:	"Adrian McMenamin" <adrianmcmenamin@...il.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, lethal@...rs.sourceforge.net,
	marcus@...pp.se
Subject: Re: [PATCH] Fix DMA on Dreamcast

On 7/21/07, Adrian McMenamin <adrianmcmenamin@...il.com> wrote:
> On 21/07/07, Peter Bortas <bortas@...il.com> wrote:
>
> >
> > Sidenote: Does Linux handle the Dreamcast DMA errata?
> >
>
> You need to explain what you mean (at least to me!).
>
> If you mean will it degrade gracefully - not without this patch if set
> to the (correct) defconfig. With iffy settings it will.

If I remember correctly (and that's a big if since I last looked at it
in 2001) some revisions of the Dreamcast hardware would sporadically
lock up if you scheduled a new DMA request to quickly after a previous
one, even if you checked the ready bit. It's worked around by a delay
of X microseconds as recommended by Sega engineers. I don't remember
the value of X, nor where exactly in the flow this workaround should
be applied.

Adding Marcus in case he has a better memory than me.

-- 
Peter Bortas
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