linux-kernel - Re: [PATCH 5/6] dmaengine: omap-dma: Remove mapping between virtual channels and requests

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Message-ID: <54ECAE75.3070501@ti.com>
Date:	Tue, 24 Feb 2015 19:01:41 +0200
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	<vinod.koul@...el.com>, Tony Lindgren <tony@...mide.com>,
	<grant.likely@...aro.org>, <dmaengine@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <robh+dt@...nel.org>,
	<nm@...com>
Subject: Re: [PATCH 5/6] dmaengine: omap-dma: Remove mapping between virtual
 channels and requests

On 02/24/2015 04:28 PM, Russell King - ARM Linux wrote:
> On Tue, Feb 24, 2015 at 04:21:22PM +0200, Peter Ujfalusi wrote:
>> Do not direct map the virtual channels to sDMA request number. When the
>> sDMA is behind of a crossbar this direct mapping can cause situations when
>> certain channel can not be requested since the crossbar request number
>> will no longer match with the sDMA request line.
>> The direct mapping for virtual channels with HW request lines will make it
>> harder to implement MEM_TO_MEM mode for the driver.
> 
> I assume when you talk about MEM_TO_MEM, you're referring to a DMA_MEMCPY
> driver.
> 
> mem2mem should not be handled by the slave driver.  This should be a
> separate DMA engine driver structure which does not have DMA_SLAVE set.
> 
> See how amba-pl08x handles this.

Thanks for the pointer. I'm just planning to add the DMA_MEMCPY support for
omap-dma. With that in place we can convert the remaining legacy API users to
use dmaengine (as I recall all of them are using DMA for memcopy)

-- 
Péter
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