Re: [PATCH/RFC v2 1/7] spi: Document DT bindings for SPI controllers in slave mode

[Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Mon, Sep 12, 2016 at 10:50:40PM +0200, Geert Uytterhoeven wrote:
> Signed-off-by: Geert Uytterhoeven <geert+renesas-gXvu3+zWzMSzQB+pC5nmwQ@public.gmane.org>
> ---
> v2:
>   - Do not create a child node in SPI slave mode. Instead, add an
>     "spi-slave" property, and put the mode properties in the controller
>     node.
> ---
>  Documentation/devicetree/bindings/spi/spi-bus.txt | 34 ++++++++++++++---------
>  1 file changed, 21 insertions(+), 13 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
> index 17822860cb98c34d..1ae28d7cafb68dc5 100644
> --- a/Documentation/devicetree/bindings/spi/spi-bus.txt
> +++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
> @@ -1,17 +1,23 @@
>  SPI (Serial Peripheral Interface) busses
>  
> -SPI busses can be described with a node for the SPI master device
> -and a set of child nodes for each SPI slave on the bus.  For this
> -discussion, it is assumed that the system's SPI controller is in
> -SPI master mode.  This binding does not describe SPI controllers
> -in slave mode.
> +SPI busses can be described with a node for the SPI controller device
> +and a set of child nodes for each SPI slave on the bus.  The system's SPI
> +controller may be described for use in SPI master mode or in SPI slave mode,
> +but not for both at the same time.
>  
> -The SPI master node requires the following properties:
> +The SPI controller node requires the following properties:
> +- compatible      - name of SPI bus controller following generic names
> +		recommended practice.

We'll probably need some way to define what interface/protocol 
the slave has. Perhaps the most specific compatible should be the 
protocol the slave uses? Maybe that is how you use a child node?

> +
> +In master mode, the SPI controller node requires the following additional
> +properties:
>  - #address-cells  - number of cells required to define a chip select
>  		address on the SPI bus.
>  - #size-cells     - should be zero.
> -- compatible      - name of SPI bus controller following generic names
> -		recommended practice.
> +
> +In slave mode, the SPI controller node requires one additional property:
> +- spi-slave       - Empty property.
> +
>  No other properties are required in the SPI bus node.  It is assumed
>  that a driver for an SPI bus device will understand that it is an SPI bus.
>  However, the binding does not attempt to define the specific method for
> @@ -21,7 +27,7 @@ assumption that board specific platform code will be used to manage
>  chip selects.  Individual drivers can define additional properties to
>  support describing the chip select layout.
>  
> -Optional properties:
> +Optional properties (master mode only):
>  - cs-gpios	  - gpios chip select.
>  - num-cs	  - total number of chipselects.
>  
> @@ -41,12 +47,14 @@ cs1 : native
>  cs2 : &gpio1 1 0
>  cs3 : &gpio1 2 0
>  
> -SPI slave nodes must be children of the SPI master node and can
> -contain the following properties.
> -- reg             - (required) chip select address of device.
> +In master mode, SPI slave nodes must be children of the SPI controller node.
> +In slave mode, the (single) slave device is represented by the controller node
> +itself. SPI slave nodes can contain the following properties.

I find this a bit confusing as you talk about master mode, then slave 
mode, then slave nodes (master mode again).

> +- reg             - (required, master mode only) chip select address of device.
>  - compatible      - (required) name of SPI device following generic names
>  		recommended practice.
> -- spi-max-frequency - (required) Maximum SPI clocking speed of device in Hz.
> +- spi-max-frequency - (required, master mode only) Maximum SPI clocking speed
> +		of device in Hz.
>  - spi-cpol        - (optional) Empty property indicating device requires
>  		inverse clock polarity (CPOL) mode.
>  - spi-cpha        - (optional) Empty property indicating device requires
> -- 
> 1.9.1
> 
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