linux-kernel - Re: [PATCH] ARM: dts: sunxi: Add num-cs for A20 spi nodes

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Message-Id: <20161125220752.c989c85e01ed202be0485c78@bidouilliste.com>
Date:   Fri, 25 Nov 2016 22:07:52 +0100
From:   Emmanuel Vadot <manu@...ouilliste.com>
To:     Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     mark.rutland@....com, devicetree@...r.kernel.org,
        linux@...linux.org.uk, linux-kernel@...r.kernel.org, wens@...e.org,
        robh+dt@...nel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: dts: sunxi: Add num-cs for A20 spi nodes

On Fri, 25 Nov 2016 16:20:47 +0100
Maxime Ripard <maxime.ripard@...e-electrons.com> wrote:

> On Thu, Nov 24, 2016 at 09:05:09PM +0100, Emmanuel Vadot wrote:
> > On Thu, 24 Nov 2016 20:55:17 +0100
> > Maxime Ripard <maxime.ripard@...e-electrons.com> wrote:
> > 
> > > On Tue, Nov 22, 2016 at 06:06:16PM +0100, Emmanuel Vadot wrote:
> > > > The spi0 controller on the A20 have up to 4 CS (Chip Select) while the
> > > > others three only have 1.
> > > > Add the num-cs property to each node.
> > > > 
> > > > Signed-off-by: Emmanuel Vadot <manu@...ouilliste.com>
> > > 
> > > I don't think we have any code that uses it at the moment. What is the
> > > rationale behind this patch?
> > > 
> > > Thanks!
> > > Maxime
> > > 
> > > -- 
> > > Maxime Ripard, Free Electrons
> > > Embedded Linux and Kernel engineering
> > > http://free-electrons.com
> > 
> >  Hi Maxime,
> > 
> >  If num-cs isn't present nothing prevent to start a transfer with a
> > non-valid CS pin, resulting in an error.
> >  num-cs are default property especially made for this and a SPI driver
> > should try to get the property at probe/attach time.
> 
> Yes, but as far as I know, our driver doesn't. I'm all in for having
> support for that in our driver, but without it, that patch is kind of
> useless.
> 
> Maxime
> 
> -- 
> Maxime Ripard, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com

 Yes the Linux driver doesn't use it but my upcoming one for FreeBSD
uses it. So it is not useless for downstream user of DTS.

 Cheers,

-- 
Emmanuel Vadot <manu@...ouilliste.com> <manu@...ebsd.org>