Subject: [PATCH 1/6] dmaengine: Add fly-by transfer flag to slave configuration structure

From: [email-masked] (Vinod Koul)
Date: Fri, 2 May 2014 21:17:37 +0530

On Fri, May 02, 2014 at 09:16:34PM +0530, Vinod Koul wrote:
+ Dan

Pls cc Dan as well

~Vinod

> On Tue, Apr 15, 2014 at 05:13:32PM +0200, Laurent Pinchart wrote:
> > Fly-by transfer mode cuts down the number of bus transactions by letting
> > the slave drive or latch the memory data bus during memory transactions
> ??            ^^^^^^^^^^^
> > instead of performing a dedicated transaction to read data from or write
> /								^^^^
> > data to the slave.
> > 
> > Support for fly-by mode by adding a new flag field to struct
> > dma_slave_config.
> > 
> > Signed-off-by: Laurent Pinchart <[email-masked]>
> > ---
> >  include/linux/dmaengine.h | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > index c5c92d5..ae99153 100644
> > --- a/include/linux/dmaengine.h
> > +++ b/include/linux/dmaengine.h
> > @@ -304,6 +304,17 @@ enum dma_slave_buswidth {
> >  };
> >  
> >  /**
> > + * enum dma_slave_flags - DMA slave configuration flags
> > + * @DMA_SLAVE_FLAG_FLY_BY - perform DMA transfers for the slave in fly-by mode.
> > + *   Instead of performing a bus transaction to read (write) data from (to) the
> > + *   slave, let the slave drive (latch) the memory bus data signals during the
> > + *   memory write (read) transaction.
> > + */
> > +enum dma_slave_flags {
> > +	DMA_SLAVE_FLAG_FLY_BY = (1 << 0),
> > +};
> > +
> > +/**
> >   * struct dma_slave_config - dma slave channel runtime config
> >   * @direction: whether the data shall go in or out on this slave
> >   * channel, right now. DMA_MEM_TO_DEV and DMA_DEV_TO_MEM are
> > @@ -333,6 +344,7 @@ enum dma_slave_buswidth {
> >   * @slave_id: Slave requester id. Only valid for slave channels. The dma
> >   * slave peripheral will have unique id as dma requester which need to be
> >   * pass as slave config.
> > + * @flags: DMA slave flags, a combination of enum dma_slave_flags flags.
> >   *
> >   * This struct is passed in as configuration data to a DMA engine
> >   * in order to set up a certain channel for DMA transport at runtime.
> > @@ -361,6 +373,7 @@ struct dma_slave_config {
> >  	u32 dst_maxburst;
> >  	bool device_fc;
> >  	unsigned int slave_id;
> > +	u32 flags;
> >  };
> I am not sure about this. Should we have a generic flag for this or just add a
> bool for fly_by mode?
> 
> Suggestions?
> 
> -- 
> ~Vinod
> 

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