linux-kernel - Re: [PATCH 5/7 v2] dma: sh: use an integer slave ID to improve API compatibility

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Message-ID: <1342431452.1726.54.camel@vkoul-udesk3>
Date:	Mon, 16 Jul 2012 15:07:32 +0530
From:	Vinod Koul <vinod.koul@...ux.intel.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Magnus Damm <magnus.damm@...il.com>, linux-sh@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7 v2] dma: sh: use an integer slave ID to improve API
 compatibility

On Mon, 2012-07-16 at 10:47 +0200, Guennadi Liakhovetski wrote:
> > I want to know what does ccr and mid_rid mean to dmac here?
> 
> CHCR contains a few fields, some enable various interrupt sources, some 
> specify repeat- and renew-modes, others yet specify transfer size, source 
> and destination address-modes (incrementing, constant, decrementing), 
> others yet select a DMA client category (slave / memcpy / ...), and a 
> transfer flag. Some of these fields could be calculated, others are 
> pre-defined for various slaves, the exact layout of those fields can also 
> vary between SoCs.
I do not understand how clients would provide these values. 
For pre-defined values, they should be dmac property why should client
like spi or mmc have clue about it?

For others like you mentioned, i guess they could be easily calculated,
right?

> MID_RID is actually a slave-selector, it contains a magic value, that 
> cannot be calculated. 
and again, how does client know this?

-- 
~Vinod

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