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Date:	Fri, 7 Mar 2014 10:48:41 +0800
From:	Mark Brown <>
To:	Charles Keepax <>
Subject: Re: [PATCH] spi/s3c64xx: Update DT binding documentation to match

On Thu, Mar 06, 2014 at 05:05:39PM +0000, Charles Keepax wrote:

> The following patch added support for spi controllers with a dedicated
> chip select pin:
> commit 3146beec21b64f4551fcf0ac148381d54dc41b1b
> spi: s3c64xx: Added provision for dedicated cs pin
> It updated the device tree binding to require a "cs-gpio" property to be
> specified on the spi controller node if chip selects will be given as
> GPIOs per slave, rather than the controller having a dedicated internal
> chip select pin.

No, it doesn't - it's saying that if the device has a "cs-gpio" property
then to use that as the chip select.  It's not a boolean, it's a GPIO
specifier.  Looking at the code it looks like the intention is to search
all children for a cs-gpio during the controller probe, it's possible
that this isn't working correctly.

> Apologies if I missed something but there are a couple of
> things I am not sure about in the original patch, there
> seems to be no special handling for the dedicated case, like
> set a bit that enables this or some such, which implies that
> parts with dedicated cs pins will always update them even
> if cs-gpio is specified. In which case wasn't what existed
> before reasonable?

The chip select signal within the IP always needs to be manipulated for
the hardware to work regardless of a GPIO being used, if a GPIO is being
used as the actual chip select then the expecation is that the pinmux
will be set up so that the signal isn't actually brought out of the

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