linux-kernel - Re: [PATCH] serial: sh-sci: don't filter on DMA device, use only channel ID

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Date:	Thu, 8 Sep 2011 03:07:53 +0530
From:	"Koul, Vinod" <vinod.koul@...el.com>
To:	"g.liakhovetski@....de" <g.liakhovetski@....de>
CC:	"Williams, Dan J" <dan.j.williams@...el.com>,
	"magnus.damm@...il.com" <magnus.damm@...il.com>,
	"lethal@...ux-sh.org" <lethal@...ux-sh.org>,
	"linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"damm@...nsource.se" <damm@...nsource.se>
Subject: Re: [PATCH] serial: sh-sci: don't filter on DMA device, use only
 channel ID

On Wed, 2011-09-07 at 22:01 +0200, Guennadi Liakhovetski wrote:
> On Thu, 8 Sep 2011, Koul, Vinod wrote:
> You're seriously suggesting to export and use an additional shdma private 
> function, bypassing the dmaengine API?... That really doesn't sound like a 
> good idea to me, sorry. How about using .device_control(DMA_SLAVE_CONFIG) 
> from the filter function directly to verify channel suitability?
Yes see stedma40, coh90138 drivers
.device_control is not right place as channel is already allocated.

You are basically moving filter fn from all clients to dmac driver.

> 
> > I cant agree to the whole point of filtering in alloc
> > 
> > One channel is allocated, we should _not_ do any further filtering
> 
> Sorry, I do not understand this argumentation. Filtering and resource 
> allocation are parts of the channel-acquisition process, either of them 
> can fail, in which case the channel remains free for future requests.
DMA drivers set caps for each channel
Client requests a channel and dmaengine matches channel based on caps
and filer function is called so that additional filtering can take
place.
And .alloc_chan_resources is supposed to allocate the channel resource
and not do anything else.

--
~Vinod