linux-kernel - Re: [PATCH/RFC] dmaengine: add a slave parameter to __dma_request

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Date:	Mon, 19 Mar 2012 15:09:37 +0100 (CET)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Vinod Koul <vinod.koul@...el.com>
cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org,
	'Jassi Brar' <jassisinghbrar@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Paul Mundt <lethal@...ux-sh.org>
Subject: Re: [PATCH/RFC] dmaengine: add a slave parameter to __dma_request_channel()

On Mon, 19 Mar 2012, Vinod Koul wrote:

> On Mon, 2012-03-19 at 14:38 +0100, Guennadi Liakhovetski wrote:
> > On Mon, 19 Mar 2012, Vinod Koul wrote:
> > 
> > > On Mon, 2012-03-19 at 12:47 +0100, Guennadi Liakhovetski wrote:
> > > > As I wrote in a reply to Linus W - you need to pass information about the 
> > > > requesting client to the dmaengine core to let it match it against mapping 
> > > > tables. 
> > > NO. 
> > > The client only needs to say that he needs a channel for DMA_SLAVE
> > 
> > How?
> Did you miss our earlier discussion on 

No, I did not.

> https://lkml.org/lkml/2012/3/8/26
> 
> Perhaps, I can enlighten you will below excerpt where we proposed to
> add:
> 
> int dmaengine_add_channel_map(struct dmaengine_map *map, unsigned int num_entries)
> {
> 	/* store this map into dmaengine and use for channle allocation */
> }
> 
> So dmaengine knows client A can use DMAC P, channel 2 and 3.

I understand this.

> So first request will receive ch 2 for A and second one will yield 3.
> 
> > 
> > 	dma_request_channel(mask, filter_fn, filter_arg)
> > 
> > Where shall the client pass to dmaengine its identity info?
> Only change I see for above to tell which client is requesting, so we
> may have to add device pointer of client while requesting.

YES! This is exactly what I am talking about! We need an additional 
parameter to dma_request_channel(). Whereas in the discussion, that you 
pointed me to, it still had the same 3 parameters, as now. (Maybe this has 
already been decided upon before - to add an additional parameter, not 
sure anymore, this thread has become too long and too slow... My apologies 
in this case) So, this can be a device pointer or some specialised slave 
ID. Device pointer is nice, I agree. And the next change, that I'd like to 
request is pass this parameter further on to DMA device driver's 
.device_alloc_chan_resources() method.

Thanks
Guennadi

> > 
> > > DMAengine will know for this client, the platform channel map (already
> > > given to it by platform) says that we can give it DMAC X, channel 4
> > > only.
> > 
> > Some clients need multiple channels - Tx, Rx,...
> > 
> > Thanks
> > Guennadi
> > 
> > > So see if it free, if so allocate it and give to client (while
> > > doing usual stuff)
> > > > You have to pass this information with the dma_request_channel() 
> > > > function. So, either you need to add a parameter or you have to reuse one 
> > > > of existing ones, e.g., deprecate the filter and use its argument for this 
> > > > purpose. If you do this and as long as you pass that parameter further on 
> > > > to the dmaengine device (controller) driver after whatever matching you 
> > > > like to do in the core - I'm fine with that, that fits well with my 
> > > > initial proposal.
> > > I don't care about filter, it can go away if it is not required.
> > > 
> > > Passing slave_config is *enhancement* so for (hopefully) last time
> > >  a) it has *nothing* to do with getting a channel, no role to play in
> > > generic scheme of things
> > >  b) it allows client to call one api for get+configure thats all! 
> > > 
> > > -- 
> > > ~Vinod
> > > 
> > 
> > ---
> > Guennadi Liakhovetski, Ph.D.
> > Freelance Open-Source Software Developer
> > http://www.open-technology.de/
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@...r.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> 
> 
> -- 
> ~Vinod
> 

---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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