From: Vinod Koul <vinod.koul@intel.com>
To: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>,
linux-kernel@vger.kernel.org,
"'Jassi Brar'" <jassisinghbrar@gmail.com>,
Linus Walleij <linus.walleij@linaro.org>,
Magnus Damm <magnus.damm@gmail.com>,
Paul Mundt <lethal@linux-sh.org>
Subject: Re: [PATCH/RFC] dmaengine: add a slave parameter to __dma_request_channel()
Date: Thu, 08 Mar 2012 18:28:33 +0530 [thread overview]
Message-ID: <1331211513.4657.67.camel@vkoul-udesk3> (raw)
In-Reply-To: <1331206459.4657.59.camel@vkoul-udesk3>
On Thu, 2012-03-08 at 17:04 +0530, Vinod Koul wrote:
> On Thu, 2012-03-08 at 12:22 +0100, Guennadi Liakhovetski wrote:
> > On Thu, 8 Mar 2012, Vinod Koul wrote:
> >
> > > On Thu, 2012-03-08 at 11:16 +0100, Guennadi Liakhovetski wrote:
> > > > I still have the impression, that my specific use-case (sh-mobile), where
> > > > channels can be freely configured for use by _ANY_ client on one of
> > > > _SEVERAL_ DMAC instances, is not fully understood or taken into account.
> > > > For this driver any kind of fixed mapping means, that we'd have to use
> > > > both virtual channels and controllers, adding _a lot_ of complexity to the
> > > > DMAC driver and making the dmaengine core just an "obfuscation layer."
> > > > Yes, I remember Russell proposing core helpers for this. They would help,
> > > > but (1) when would they be available, (2) how well would they be suitable
> > > > for us, (3) they'd take the coding / maintainance burden away, but
> > > > wouldn't reduce complexity and run-time overhead.
> > > Lets try to address you case as well.
> > > On a typical platform
> >
> > Let's take the mackerel board with the sh7372 SoC. it's not the state of
> > the art, but that's what I'm currently working with and it should give us
> > a good enough idea
> >
> > > 1) how many dma controllers you have?
> >
> > currently supported 5 of 3 types (3 of type A, 1 of each of the types B
> > and C), all handled by the same driver
> >
> > > 2) how many clients you have
> >
> > huh... many. Maybe like 20 or more, and more, that are not yet supported,
> > using type A, and 1 for each of types B and C
> >
> > > 3) which client can use what controller channel? How is mapping decided,
> > > do you have a mux, is it hard wired by soc designers,....?
> >
> > In general - with all the current sh-mobile hardware, that I'm aware of -
> > there can be several controller instances on an SoC of each controller
> > type. Inside each type all instances and all channels are freely
> > configurable. So, of 20 Type A clients they can use any channels on any
> > one of the 3 type A controllers. Types B and C are "degenerate" cases,
> > there clients are practically hard-wired to a specific DMA controller.
> >
> > So, we don't have to decide on mappings for type A. We just pick up any
> > free channels on any controller and configure them accordingly. Whether
> > there's a mux somewhere - you can say so, but it's all inside the SoC, and
> > it's configured automatically ones you configure a physical channel to
> > serve a specific client.
> >
> > > Can you pls give a description so that we ensure all models fit in the
> > > final solution?
> >
> > That's what I've been trying to do since several days now... I've been
> > saying "multiple controllers with multiple channels all freely
> > configurable for any device from a list" again and again... Seems I'm
> > speaking some strange language, that noone understands.
> Okay. One more question before I can tell you how it can work for you
> without you sweating it out :-)
>
> So you have:
> case A: Here you have N dmacs and M controllers, any controller can use
> any channel, No constraints on channel assignments, right?
> case B: Some hardwired controllers P which can only be used by a set
> clients Q?
>
> Anything else I missed in your description?
Assuming I didn't miss...
The case B can be handled without sweat by platforms channel mapping
information.
Case A where we don't find that devices exist in map, thus being treated
as generic DMA channels and can be handled easily in sequence. So when
someone in Q request a channel it would get first channel in Ps
This way we handle both of them in a transparent manner to both clients
and controllers.
Perhaps we can also add capability to know that if channel is to be
searched in map or not - would be anyway required for non slave cases.
--
~Vinod
next prev parent reply other threads:[~2012-03-08 12:53 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-01 15:26 [PATCH/RFC] dmaengine: add a slave parameter to __dma_request_channel() Guennadi Liakhovetski
2012-03-02 13:21 ` Guennadi Liakhovetski
2012-03-06 8:30 ` Vinod Koul
2012-03-06 8:53 ` Guennadi Liakhovetski
2012-03-06 12:08 ` Vinod Koul
2012-03-06 13:03 ` Guennadi Liakhovetski
2012-03-07 6:28 ` Vinod Koul
2012-03-07 9:18 ` Guennadi Liakhovetski
2012-03-07 9:30 ` Russell King - ARM Linux
2012-03-07 9:55 ` Linus Walleij
2012-03-07 10:02 ` Guennadi Liakhovetski
2012-03-07 10:31 ` Russell King - ARM Linux
2012-03-07 12:30 ` Guennadi Liakhovetski
2012-03-07 12:45 ` Guennadi Liakhovetski
2012-03-07 12:46 ` Russell King - ARM Linux
2012-03-07 13:49 ` Guennadi Liakhovetski
2012-03-07 14:26 ` Russell King - ARM Linux
2012-03-07 15:44 ` Guennadi Liakhovetski
2012-03-07 16:27 ` Russell King - ARM Linux
2012-03-07 18:21 ` Guennadi Liakhovetski
2012-03-08 6:30 ` Vinod Koul
2012-03-08 10:16 ` Guennadi Liakhovetski
2012-03-08 10:55 ` Vinod Koul
2012-03-08 11:22 ` Guennadi Liakhovetski
2012-03-08 11:34 ` Vinod Koul
2012-03-08 12:58 ` Vinod Koul [this message]
2012-03-08 13:18 ` Guennadi Liakhovetski
2012-03-09 9:21 ` Vinod Koul
2012-03-09 9:24 ` Guennadi Liakhovetski
2012-03-09 9:39 ` Vinod Koul
2012-03-09 12:20 ` Guennadi Liakhovetski
2012-03-09 14:07 ` Russell King - ARM Linux
2012-03-09 14:15 ` Guennadi Liakhovetski
2012-03-12 2:47 ` Vinod Koul
2012-03-12 19:47 ` Linus Walleij
2012-03-16 9:36 ` Guennadi Liakhovetski
2012-03-16 10:16 ` Linus Walleij
2012-03-16 10:31 ` Russell King - ARM Linux
2012-03-16 11:09 ` Guennadi Liakhovetski
2012-03-16 14:11 ` Linus Walleij
2012-03-16 14:28 ` Guennadi Liakhovetski
2012-03-30 5:44 ` Linus Walleij
2012-03-30 6:40 ` Guennadi Liakhovetski
2012-03-30 10:38 ` Russell King - ARM Linux
2012-04-03 20:36 ` Linus Walleij
2012-04-03 20:44 ` Linus Walleij
2012-04-12 21:33 ` Guennadi Liakhovetski
2012-04-12 23:48 ` Russell King - ARM Linux
2012-03-30 10:29 ` Russell King - ARM Linux
2012-03-30 10:40 ` Guennadi Liakhovetski
2012-03-30 10:43 ` Russell King - ARM Linux
2012-03-19 11:58 ` Vinod Koul
2012-03-30 10:25 ` Russell King - ARM Linux
2012-03-19 11:39 ` Vinod Koul
2012-03-19 11:37 ` Vinod Koul
2012-03-19 11:47 ` Guennadi Liakhovetski
2012-03-19 13:34 ` Vinod Koul
2012-03-19 13:38 ` Guennadi Liakhovetski
2012-03-19 14:00 ` Vinod Koul
2012-03-19 14:09 ` Guennadi Liakhovetski
2012-03-19 14:22 ` Vinod Koul
2012-03-19 14:45 ` Guennadi Liakhovetski
2012-03-19 16:20 ` Vinod Koul
2012-03-19 16:32 ` Guennadi Liakhovetski
2012-03-20 7:11 ` Vinod Koul
2012-03-08 11:46 ` Linus Walleij
2012-03-08 12:36 ` Guennadi Liakhovetski
2012-03-07 16:31 ` Linus Walleij
2012-03-07 16:20 ` Linus Walleij
2012-03-07 9:46 ` Linus Walleij
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