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

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Date:	Thu, 26 Jul 2007 12:10:30 +0200
From:	Marcus Comstedt <marcus@...pp.se>
To:	"Peter Bortas" <bortas@...il.com>
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


"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)?


  // Marcus


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