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

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Message-ID: <20161201092150.rlo5skxd6elovlgq@lukather>
Date:   Thu, 1 Dec 2016 10:21:50 +0100
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Emmanuel Vadot <manu@...ouilliste.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

Hi Emmanuel,

On Fri, Nov 25, 2016 at 10:07:52PM +0100, Emmanuel Vadot wrote:
> 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.
> 
>  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.

Ah, I didn't know this was for FreeBSD. So you started to use our DTs,
or do you have some modifications to it? How does that work?

Anyway, the fact that it isn't used by our driver at the moment and
that it's meant for other OSes should be mentionned in the commit log.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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