linux-kernel - Re: [PATCH 2/8] dmaengine: Add flow controller information to dma_slave

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Date:	Tue, 17 Jan 2012 09:37:14 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Viresh Kumar <viresh.kumar@...com>
Cc:	vinod.koul@...el.com, dan.j.williams@...el.com,
	linux@....linux.org.uk, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, armando.visconti@...com,
	shiraz.hashim@...com, vipin.kumar@...com, rajeev-dlh.kumar@...com,
	deepak.sikri@...com, vipulkumar.samar@...com, amit.virdi@...com,
	pratyush.anand@...com, bhupesh.sharma@...com,
	viresh.linux@...il.com, bhavna.yadav@...com,
	vincenzo.frascino@...com, mirko.gardi@...com
Subject: Re: [PATCH 2/8] dmaengine: Add flow controller information to dma_slave_config

On Mon, Jan 16, 2012 at 10:50 AM, Viresh Kumar <viresh.kumar@...com> wrote:

> Flow controller is programmable for few controllers and there are few
> intelligent peripherals like, Synopsys JPEG controller, that needs to be a flow
> controller of DMA transfers on dest side.
>
> For this, currently two drivers, pl08x and dw_dmac, support flow controller to
> be passed from platform to these drivers.

OK

> Perhaps, this should be a part of struct dma_slave_config. This patch adds
> another field device_fc to this structure. User drivers must pass this as true
> if they want to be flow controller of certain transfers.

I dma_slave_config is supposed to be about info that

1) Must to be set-up at runtime
2) All DMA controllers need to know

So if it doesn't *have* to be set up by drivers at runtime, please keep it in
platform data.

If it is (1), so you have a use case where you have to switch a certain channel
between DMA master and device flow control at run-time it looks like it could
be useful for others as well, but I doubt this so I'd like some back-up on
that.

Yours,
Linus Walleij
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