linux-kernel - Re: [PATCH 1/5] spi: do not fail if the CS line is not connected

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Date:	Fri, 17 Jun 2016 13:28:03 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Andi Shyti <andi@...zian.org>
Cc:	Andi Shyti <andi.shyti@...sung.com>, Kukjin Kim <kgene@...nel.org>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/5] spi: do not fail if the CS line is not connected

On Fri, Jun 17, 2016 at 08:36:22PM +0900, Andi Shyti wrote:

> > > 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.

> This is the case of:

> ./drivers/spi/spi-mpc52xx-psc.c:391: master->num_chipselect = 255;
> ./drivers/spi/spi-oc-tiny.c:256:        master->num_chipselect = 255;

> ./drivers/spi/spi-pxa2xx-pci.c:64:              .num_chipselect = -1,
> ./drivers/spi/spi-bcm2835aux.c:436:     master->num_chipselect = -1;

These need fixing.

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