From mboxrd@z Thu Jan  1 00:00:00 1970
From: geert@linux-m68k.org (Geert Uytterhoeven)
Date: Wed, 6 Aug 2014 09:17:57 +0200
Subject: DMA engine API issue (was: [PATCH/RFC 0/5] R-Car Gen2 DMAC
 hardware descriptor list support)
In-Reply-To: <1877927.dGcJCfKbeH@avalon>
References: <1406032431-3807-1-git-send-email-laurent.pinchart+renesas@ideasonboard.com>
 <2568292.I2Yo4lJlu6@avalon>
 <20140804175458.GH30282@n2100.arm.linux.org.uk>
 <1877927.dGcJCfKbeH@avalon>
Message-ID: <CAMuHMdVz8hNus5x1hn0feqb1SYsUuhA4QHHfPGyebiKLZJwfEQ@mail.gmail.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Hi Laurent,

On Wed, Aug 6, 2014 at 1:19 AM, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
> I actually have the opposite problem, in my case channels of physically
> separate DMA engines can be used interchangeably to serve the system's slaves.
> Using the DMA engine DT bindings, DT nodes of the slaves currently reference a
> specific DMA engine, even if they can be served by both. This leads to limited
> dynamic channel allocation capabilities (especially when taking into account
> lazy channel allocation as mentioned in another mail in this thread).

What about adding a property to the first one, referencing the second
(or the other way around, don't know what's the easiest to implement)?

        dmac0: dma-controller at e6700000 {
                ...
                renesas,alternative = <&dmac1>;
                ...
        };

        dmac1: dma-controller at e6720000 {
                ...
        };

That would avoid having to bind a slave device explicitly to a single
dmac, or having to bind all slave devices to all dmacs.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds