linux-kernel - Re: [PATCH 01/14] dma: sun6i-dma: Add burst case of 4

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Message-Id: <20161004154651.3d0eb02badb6dc66758dd3aa@free.fr>
Date:   Tue, 4 Oct 2016 15:46:51 +0200
From:   Jean-Francois Moine <moinejf@...e.fr>
To:     Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:     Mylène Josserand 
        <mylene.josserand@...e-electrons.com>, vinod.koul@...el.com,
        maxime.ripard@...e-electrons.com, wens@...e.org,
        mturquette@...libre.com, sboyd@...eaurora.org, lgirdwood@...il.com,
        broonie@...nel.org, perex@...ex.cz, tiwai@...e.com,
        lee.jones@...aro.org, mark.rutland@....com, robh+dt@...nel.org,
        devicetree@...r.kernel.org, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com,
        alexandre.belloni@...e-electrons.com, dmaengine@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 01/14] dma: sun6i-dma: Add burst case of 4

On Tue, 4 Oct 2016 14:12:21 +0200
Thomas Petazzoni <thomas.petazzoni@...e-electrons.com> wrote:

> > > Add the case of a burst of 4 which is handled by the SoC.
> > > 
> > > Signed-off-by: Mylène Josserand <mylene.josserand@...e-electrons.com>
> > > ---
> > >  drivers/dma/sun6i-dma.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> > > index 8346199..0485204 100644
> > > --- a/drivers/dma/sun6i-dma.c
> > > +++ b/drivers/dma/sun6i-dma.c
> > > @@ -240,6 +240,8 @@ static inline s8 convert_burst(u32 maxburst)
> > >  	switch (maxburst) {
> > >  	case 1:
> > >  		return 0;
> > > +	case 4:
> > > +		return 1;
> > >  	case 8:
> > >  		return 2;
> > >  	default:
> > > -- 
> > > 2.9.3  
> > 
> > This patch has already been rejected by Maxime in the threads
> > 	http://www.spinics.net/lists/dmaengine/msg08610.html
> > and
> > 	http://www.spinics.net/lists/dmaengine/msg08719.html
> > 
> > I hope you will find the way he wants for this maxburst to be added.
> 
> I was about to reply to Mylene's e-mail, suggesting that she should add
> a comment in the code (and maybe in the commit log) to explain why this
> addition is needed, and also that even though the schematics say that
> value "1" (max burst size of 4 bytes) is reserved, it is in fact
> incorrect. The Allwinner BSP code is really using this value, and it's
> the value that makes audio work, so we believe the datasheet is simply
> incorrect.
> 
> We already discussed it with Maxime, so I believe he should agree this
> time. But I would suggest to have such details explained in the commit
> log and in a comment in the code.

Strange. Looking at the datasheets of the A23, A31, A33, A83T and H3
(these are the SoCs using the DMA sun6i), only the H3 can have 4 as the
burst size (the doc is unclear for the A31).

Well, I was submitting for the H3, Mylène is submitting for the A33.
So, what about the A23, A31 and A83T?

-- 
Ken ar c'hentañ	|	      ** Breizh ha Linux atav! **
Jef		|		http://moinejf.free.fr/