Re: [PATCH 2/2] dt/bindings: control CS via standard GPIO operations instead of SPI-HW

On 17.03.2015, at 04:18, Stephen Warren [off-list ref] wrote:

quoted

But then it means in principle that this is a more general issue
that just became apparent now.

Yes.

...

quoted

So this is maybe the way forward for the whole default-dt?

For SPI it would look like this:
&gpio {
       spi0_pins: spi0_pins {
               brcm,pins = <7 8 9 10 11>;
               brcm,function = <4>; /* alt0 */
       };
	...
}

&spi0 {
	...
       pinctrl-0 = <&spi0_pins>;
	...
}

And if you keep spi0 disabled in the dtsi files then the ALT
modes should not be set.

Yes, so long as it's disabled by default that would be OK. However, I
wonder why we don't just rely on the firmware to set up the pinmux,
since as you mentioned it does it now?

...

quoted

Obviously we could also split the gpio-block into 
"normal SPI" and "CS" pins, which would allow changing the
"defaults" also in the dts that gets build.

So how should we proceed?

If we do put any default CS GPIO setup in the kernel DT, we should
indeed put it into a separate node (pinctrl state) so that the user can
override it easily without any interactions with any other pins/...

So I will create a patch to separate the spi portions out as 
mentioned above.

I will actually create 2 gpio-sections:
one for the SPI transfer pins (GPIO 9, 10, 11) 
and one for the chipselects (8, 7), which can get overridden
either as output or as ALT0 in a customized device tree.

SPI by default shall be disabled.

Martin
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