linux-kernel - Re: [PATCH 2/4] dmaengine: vdma: Add support for mulit-channel dma mode

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Date:	Tue, 28 Jun 2016 10:04:59 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Appana Durga Kedareswara Rao <appana.durga.rao@...inx.com>
Cc:	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	Michal Simek <michals@...inx.com>,
	Soren Brinkmann <sorenb@...inx.com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"moritz.fischer@...us.com" <moritz.fischer@...us.com>,
	"laurent.pinchart@...asonboard.com" 
	<laurent.pinchart@...asonboard.com>,
	"luis@...ethencourt.com" <luis@...ethencourt.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>
Subject: Re: [PATCH 2/4] dmaengine: vdma: Add support for mulit-channel dma
 mode

On Wed, Jun 22, 2016 at 07:04:28AM +0000, Appana Durga Kedareswara Rao wrote:
> > > >
> > > > Can you elobrate what you meant by Multichannel mode? This patch
> > > > seems to do two things, one is to add interleaved dma support and
> > > > something else. Can you explain the latter part?
> > >
> > > AXI DMA has two Stream interfaces (Memory to Stream MM2S and Stream to
> > > Memory S2MM)
> > 
> > what is a stream in this context?
> 
> Stream means I/O transfer (Memory to I/O and I/O to Memory).
> Sorry if I confused you.
> 
> > 
> > > In Multi-Channel dma mode each stream interface can be configured up to 16
> > channels.
> > > In Multi-channel DMA mode IP supports only interleaved transfers (2-D
> > transfers).
> > 
> > 
> > >
> > > >
> > > > >  /**
> > > > > + * struct xilinx_mcdma_config - DMA Multi channel configuration
> > > > > +structure
> > > > > + * @tdest: Channel to operate on
> > > > > + * @tid:   Channel configuration
> > > > > + * @tuser: Tuser configuration
> > > > > + * @ax_user: ax_user value
> > > > > + * @ax_cache: ax_cache value
> > > > > + */
> > > > > +struct xilinx_mcdma_config {
> > > > > +	u8 tdest;
> > > > > +	u8 tid;
> > > > > +	u8 tuser;
> > > > > +	u8 ax_user;
> > > > > +	u8 ax_cache;
> > > >
> > > > can you describe these in details, what do these do, what are the
> > > > values to be programmed?
> > >
> > > As said above In Multi-Channel Mode each Stream interface can be
> > > Configured up to 16 channels each channel is differentiated based on the tdest
> > and tid values.
> > 
> > Then why are you not registering 16 channels for this? That should give you
> > channel to operate on!
> 
> The number of channels are configurable.
> We are registering number of Channels that h/w configured for.
> 
> Will fix in the next version. Will remove this config.
> And based on the channel type will configure the h/w.

Looking at this you should redesign!

The vchan was designed to operate on 'virtual' channels. The hardware
channels can be independent of that.

Your IP seems to be a good fit for that approach. Do not link the two and
separate them. User can have a virtual channel. In your driver, you can
manage hardware channels...

> 
> > 
> > >
> > > tdest:
> > > TDEST provides routing information for the data stream.
> > 
> > pls elobrate
> 
> Need to configure this with the channel number that
> We would like to transfer data.

This should be internal to driver...

-- 
~Vinod