linux-kernel - Re: [RFC v2 2/5] dmaengine: Add slave DMA interface

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Date:	Thu, 31 Jan 2008 15:12:47 +0100
From:	Haavard Skinnemoen <hskinnemoen@...el.com>
To:	David Brownell <david-b@...bell.net>
Cc:	Paul Mundt <lethal@...ux-sh.org>,
	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org,
	Shannon Nelson <shannon.nelson@...el.com>,
	kernel@...32linux.org, Francis Moreau <francis.moro@...il.com>,
	"Vladimir A. Barinov" <vbarinov@...mvista.com>,
	Pierre Ossman <drzeus-list@...eus.cx>
Subject: Re: [RFC v2 2/5] dmaengine: Add slave DMA interface

On Thu, 31 Jan 2008 04:51:03 -0800
David Brownell <david-b@...bell.net> wrote:
> First steps are after all followed by second steps, and often
> by third steps.  It's not "overengineering" to recognize when
> those steps necessarily have a direction.

But it might be considered overengineering to actually take those steps
when you're not sure if the direction is the right one :)

Maybe we should ask Al Viro if we can use his in-kernel XML parser and
take care of the extensibility requirements once and for all? ;-)

> In this case, that direction is "working on more hardware", so
> evaluating the interface proposal against several types of
> hardware is a good way to review it.  The hardware I referenced
> doesn't seem "fringe" to me; it's used on more Linux systems
> and by more users than the Synopsys design.  And I've seen some
> of the same issues on other DMA controllers:  priority, options
> for synchronization (e.g. after DMAREQ is signaled), and more.

Right, but can we get away with some sort of vague "I think we need to
go in _that_ direction eventually" spec for now, and just see how many
existing drivers and hardware we can support with just some basic
interfaces, and get a better idea about what we need to support the
remaining ones?

> In that vein, doesn't SuperH have DMA controllers to fit into this
> proposed interface?  I don't know about such "fringe" hardware
> myself, but it'd be good to know if this proposal is sufficient
> for the needs of drivers there.

That would indeed be good to know, and is in fact the reason why I Cc'd
Paul and Francis in the first place.

Haavard
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