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

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Date:   Thu, 24 Nov 2016 21:05:09 +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 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.

 Cheers,

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