From owner-freebsd-current  Thu Apr  4 19:25:59 2002
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Date: Thu, 4 Apr 2002 19:25:49 -0800 (PST)
From: Matthew Jacob <mjacob@feral.com>
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To: "Justin T. Gibbs" <gibbs@scsiguy.com>
Cc: Terry Lambert <tlambert2@mindspring.com>,
	Andrew Gallatin <gallatin@cs.duke.edu>, freebsd-current@freebsd.org
Subject: Re: BUS_SPACE_MAXSIZE & isp driver. 
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On Thu, 4 Apr 2002, Justin T. Gibbs wrote:

> >BUS_SPACE_MAXSIZE seems to be related to the 'largest xfer you will be allowed
> >to do at one time'- which is wrong because MAXPHYS is larger.
> 
> If you look at the x86 implementation, BUS_SPACE_MAXSIZE is only
> used in the non-GNUC case and is not referenced (I don't think)
> by any driver code.  Even setting it to MAXPHYS is not truely
> correct since at some point we will have to start supporting
> transfer mappings that are larger than what can be mapped by
> a single buffer.  I never realized that there was such controversy
> over this value... it was just put in so that I could have something
> for the non-GNUC case.

Yeah, but, uh, it'll blow up in one's face.....

The question I have is what *should* we be using? Should BUS_SPACE_MAXSIZE be
bumped up so that any dma allocation we attempt for a platform will fit within
it?

I mean, it's used in a lot of places, so clearly it must mean something,
right? What are the semantics here?

-matt



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