linux-kernel - Re: [PATCH 04/18] dmaengine/amba-pl08x: Remove redundant comment and rewrite original

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Message-ID: <20110731090619.GA30888@n2100.arm.linux.org.uk>
Date:	Sun, 31 Jul 2011 10:06:19 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	pratyush.anand@...com, rajeev-dlh.kumar@...com,
	bhupesh.sharma@...com, shiraz.hashim@...com,
	"Koul, Vinod" <vinod.koul@...el.com>, linux-kernel@...r.kernel.org,
	vipin.kumar@...com, armando.visconti@...com, amit.virdi@...com,
	vipulkumar.samar@...com, viresh kumar <viresh.linux@...il.com>,
	deepak.sikri@...com, dan.j.williams@...el.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 04/18] dmaengine/amba-pl08x: Remove redundant comment
	and rewrite original

On Sun, Jul 31, 2011 at 01:37:46AM +0200, Linus Walleij wrote:
> 2011/7/31 Russell King - ARM Linux <linux@....linux.org.uk>:
> > On Sun, Jul 31, 2011 at 12:32:55AM +0200, Linus Walleij wrote:
> >> The PL08x has two bus mastering interfaces. They can be
> >> connected to two separate busses and two adress spaces
> >> even, usually that is not the case though.
> >
> > This is not what the function is about... that's done by my
> > pl08x_select_bus() function.
> 
> To be clear, I was explaining what I percieved as a
> question from Viresh about what the comment in this hunk of
> the patch was about:

Yes, and the comment and function name are wrong for what it's doing.
I repeat: it has nothing to do with selecting an AHB bus.

> As for the LLI code, all of it's weird complexity comes from the fact
> that the DMAC cannot let a single element pass across 1KB (0x400)
> boundaries, which is one more than a little insane hardware
> restriction, and I have no clue where that limitation actually comes
> from, likely strange VHDL code.

Viresh's discussion with ARM Ltd indicates that this is not the case,
and that restriction comes from misunderstanding of the documentation.
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