linux-kernel - Re: [PATCH v2 1/2] dmaengine: dma_slave_config: add support for slave port window

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Date:   Tue, 29 Nov 2016 18:44:44 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     dan.j.williams@...el.com, tony@...mide.com, linux@...linux.org.uk,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org, arnd@...db.de
Subject: Re: [PATCH v2 1/2] dmaengine: dma_slave_config: add support for
 slave port window

On Tue, Nov 29, 2016 at 12:47:48PM +0200, Peter Ujfalusi wrote:
> Vinod,
> 
> On 11/17/2016 02:50 PM, Peter Ujfalusi wrote:
> > Some slave devices uses address window instead of single register for read
> > and/or write of data. With the src/dst_port_window_size the address window
> > can be specified and the DMAengine driver should use this information to
> > correctly set up the transfer to loop within the provided window.
> > 
> > Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> > ---
> >  include/linux/dmaengine.h | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > index cc535a478bae..689d44327ef3 100644
> > --- a/include/linux/dmaengine.h
> > +++ b/include/linux/dmaengine.h
> > @@ -336,6 +336,12 @@ enum dma_slave_buswidth {
> >   * may or may not be applicable on memory sources.
> >   * @dst_maxburst: same as src_maxburst but for destination target
> >   * mutatis mutandis.
> > + * @src_port_window_size: The length of the register area the data need to be
> > + * written on the device side. It is only used for devices which is using an
> > + * area instead of a single register to receive the data. Typically the DMA
> > + * loops in this area in order to transfer the data.
> > + * @dst_port_window_size: same as src_port_window_size but for the destination
> > + * port.
> 
> I think this needs some clarification.
> Should the src/dst_port_window_size be in bytes or in words? I think it would
> make more sense to define it as number of words to be in sync with the
> src/dst_maxburst.

Yes good catch, I would indeed prefer words here


-- 
~Vinod