From mboxrd@z Thu Jan  1 00:00:00 1970
From: andi@etezian.org (Andi Shyti)
Date: Sun, 19 Jun 2016 15:09:02 +0900
Subject: [PATCH 1/5] spi: do not fail if the CS line is not connected
In-Reply-To: <20160617122803.GN26099@sirena.org.uk>
References: <1466150245-2648-1-git-send-email-andi.shyti@samsung.com>
 <1466150245-2648-2-git-send-email-andi.shyti@samsung.com>
 <20160617104725.GC26099@sirena.org.uk>
 <20160617113622.GA10760@jack.zhora.eu>
 <20160617122803.GN26099@sirena.org.uk>
Message-ID: <20160619060902.GB424@jack.zhora.eu>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Hi Mark,

> > > > In this case do not fail and defer to the SPI device drivers the
> > > > responsibility to check whether the num-cs is '0'.
> 
> > > A SPI controller always has one chip seelct, it may not be controllable
> > > but it's at least logically present.
> 
> > This is true, but there are cases where the CS is not connected
> > and this case needs to be treated separately to allow the device
> > to work.
> 
> In what way?  It is just as easy for a device with no physical chip
> select to have a logical chip select of 0 that it does nothing with as
> it is for that device to handle any other number.

That is indeed my case: the s3c64xx doesn't send anything, unless
I manually enable CS (from the next patches I need to write '0'
in the CS register). But I need smoething to tell to the
device that the CS line is not connected, for example a flag in
the DTS.

It comes natural to me to set "num-cs = <0>" instead of defining
a new property. In this case I will consider that there is no CS
line, even though there is a CS controller.

Thanks,
Andi