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

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Date:	Tue, 24 Feb 2015 14:28:33 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
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 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.

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