linux-kernel - Re: [PATCHv4] DMAEngine: Define interleaved transfer request api

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Message-ID: <CABE8wwvSRaJBED4E+dKo_SWAF93LA+Lqqdb1agqbMcROKxYQ8Q@mail.gmail.com>
Date:	Wed, 5 Oct 2011 11:19:23 -0700
From:	"Williams, Dan J" <dan.j.williams@...el.com>
To:	Jassi Brar <jaswinder.singh@...aro.org>
Cc:	Russell King <rmk@....linux.org.uk>,
	Barry Song <21cnbao@...il.com>,
	Vinod Koul <vinod.koul@...el.com>,
	linux-kernel@...r.kernel.org,
	DL-SHA-WorkGroupLinux <workgroup.linux@....com>,
	Dave Jiang <dave.jiang@...el.com>
Subject: Re: [PATCHv4] DMAEngine: Define interleaved transfer request api

On Mon, Oct 3, 2011 at 11:23 AM, Jassi Brar <jaswinder.singh@...aro.org> wrote:
> You are assuming only Slave usage.
> src_inc/dst_inc are mainly for 'Memset' type operation.

There currently are not any users of offloaded memset in the kernel,
do you have one in mind?  Otherwise I would not design for it this
early.

> In Slave transfer they would help avoid allocating full length RX buffer
> when the client only wants to send data but the controller works
> only in full-duplex and vice-versa (thanks to RMK for pointing the case,
> and I remember S3C24XX do have such SPI controller).
> More generally when one needs to transmit the same data, or discard
> the received data, for a certain period of time.

In the slave case I would think the driver would know the address
increment attributes of the slave and would not need to be told on
each operation by the client?
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