linux-kernel - RE: [PATCHv2] wlcore: spi: add wl18xx support

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Date:	Mon, 18 Apr 2016 05:55:51 +0000
From:	"Reizer, Eyal" <eyalr@...com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Kalle Valo <kvalo@...eaurora.org>,
	Eyal Reizer <eyalreizer@...il.com>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>
Subject: RE: [PATCHv2] wlcore: spi: add wl18xx support

> >
> > - all wilink family needs special init command for entering wspi mode.
> >   extra clock cycles should be sent after the spi init command while the
> >   cs pin is high.
> > - switch to controling the cs pin from the spi driver for achieveing the
> >   above.
> > - the selected cs gpio is read from the spi device-tree node using the
> >   cs-gpios field and setup as a gpio.
> > - See the example below for specifying the cs gpio using the cs-gpios entry
> > &spi0   {
> >         ...
> >         cs-gpios = <&gpio0 5 0>;
> >         ...
> >         wlcore: wlcore@0 {
> >                 compatible = "ti,wl1835";
> >         ...
> >         ...
> >         };
> > };
> >
> > Signed-off-by: Eyal Reizer <eyalr@...com>
> 
> I don't think this can work in general: not all SPI hosts uses GPIOs for
> controlling CS, so the logic can't work, and it's also a layering violation for the
> driver to look at the parent.
> 
> I would suggest fixing this using a new API function from the SPI core, if we
> don't already have a generic way to do it.
>
Originally this is what I have done until I was pointed to the generic cs-gpio mechanism 
in the SPI core. 
It is a generic mechanism already in the SPI core driver.
See: Documentation/devicetree/bindings/spi/spi-bus.txt

It is also part of the generic spi.h (include/Linux/spi/spi.h), already part of 
" struct spi_device" So it seemed redundant adding another mechanism for 
implementing the same.
Platform that interact with a wilink need to use it, and platforms that don't  
have this capability will probably not interact with a wilink device using SPI.

Best Regards,
Eyal