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Re: [PATCH 1/2] dmaengine: TXx9 Soc DMA Controller driver

Subject: Re: [PATCH 1/2] dmaengine: TXx9 Soc DMA Controller driver
From: Atsushi Nemoto <>
Date: Thu, 26 Mar 2009 23:12:43 +0900 (JST)
In-reply-to: <>
Original-recipient: rfc822;
References: <> <> <>
On Sat, 21 Mar 2009 21:29:20 +0900 (JST), Atsushi Nemoto <> 
> > I think creating a dma_device instance per channel and specifying that
> > device like atmel-mci is the more future-proof way to go.
> Well, I have considered it but it looks overkill for me at that time.
> Maybe time to think again...
> > > And I want to call Channel-3 of DMAC-0 "dma0chan3" even if Channel-2
> > > was assigned to for public memcpy channel.
> > 
> > The problem is you could pass in the chan_id to guarantee 'chan3', but
> > there is no guarantee that you will get 'dma0', as the driver has no
> > knowledge of what other dma devices may be in the system.
> Yes, I do not expect 'dma0'.  My filter function uses
> dev_name(chan->device->dev), which is "txx9dmac.0" in this case.
> Anyway, "one dma-device per channel" manner will make things much simpler.

Unfortunately, not so simple.  If I created a dma_device for each
channel, all chan->chan_id will be 0 and all chan->device->dev points
same platform device.  This makes client driver hard to select the
particular channel.  Making a platform device for each channel will
solve this, but it looks wrong way to go for me.

So I will go back to multiple channels per device style, and try to
simplify "reservation".  While all client should know correct channel
number, the reservation is just for detecting bad configuration.

Atsushi Nemoto

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