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

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Message-ID: <7e5f60720707260559m64211206q581a4c83c9060485@mail.gmail.com>
Date:	Thu, 26 Jul 2007 14:59:51 +0200
From:	"Peter Bortas" <bortas@...il.com>
To:	"Marcus Comstedt" <marcus@...pp.se>
Cc:	"Adrian McMenamin" <adrianmcmenamin@...il.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, lethal@...rs.sourceforge.net
Subject: Re: [PATCH] Fix DMA on Dreamcast

On 7/26/07, Marcus Comstedt <marcus@...pp.se> wrote:
>
> "Peter Bortas" <bortas@...il.com> writes:
>
> > 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.
>
>
> I don't remeber any such delay.  Are you sure you're not thinking
> about the G2 bus problem (where accesses need to be programatically
> serialized, whether they are PIO or DMA)?

In that case my memory is worse than I thought. I'll see if I can dig
up my old notes.

-- 
Peter Bortas
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