Re: [PATCHv2] wlcore: spi: add wl18xx support

Arnd Bergmann
2016-04-18T14:57:18Z

On Monday 18 April 2016 05:55:51 Reizer, Eyal wrote:
> > >
> > > - 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@ti.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

The cs-gpios property is documented as optional, it defines how you should
list the gpios if CS is implemented using gpio, but not all hardware does
it like this.

> 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.

The cs_gpio field in spi_device belongs to the spi host controller, no other
slave driver uses it.

I wasn't asking for a duplication of this mechanism, but an interface to
use it properly. Internally, the spi core uses the spi_set_cs() function to
pick a CS. Find a way to use that rather than reimplementing it incorrectly.

Arnd