On 15:36-20210311, Jan Kiszka wrote:

On 11.03.21 15:21, Nishanth Menon wrote:

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On 15:14-20210311, Jan Kiszka wrote:

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See [1] compare the compatibles against
Documentation/devicetree/bindings -> I think you should describe what
your hardware really is though.

This SPI bus is routed to an Arduino connector. By default, userspace
(e.g. mraa) takes ownership and adds the desired logic for what is being
connected. We have no idea what shield or other extension the user adds,
though.

overlays look like the right approach for variable systems like these.
It is not exactly plug and play.. but it does provide a level of
flexibility that is helpful.

Yes, that's for extensions which have kernel drivers. The default model
here is userspace, though. Will add as a separate patch to our queue for
now.

My colleagues did some checkups and pulled up a few thread on spidev
of potential interests..

See:
https://patchwork.kernel.org/project/spi-devel-general/patch/1427499742-26916-1-git-send-email-broonie@kernel.org/
https://yurovsky.github.io/2016/10/07/spidev-linux-devices.html
etc...

I'd split the spidev node alone as an addendum indicate the checkpatch
warning, describe the details and loop in spidev list, Mark, et.al. to
discuss the direction. I am hoping we can get this resolved or get a
direction for .13-rc1

But that said, I see some examples such as 
for i in `git grep ".compatible" drivers/spi/spidev.c|grep =|cut -d '=' -f2|cut -d ' ' -f2`; do git grep $i Documentation/devicetree/bindings/; done

Documentation/devicetree/bindings/spi/spi-mux.yaml:                compatible = "lineartechnology,ltc2488";
Documentation/devicetree/bindings/misc/ge-achc.txt:- compatible : Should be "ge,achc"
Documentation/devicetree/bindings/misc/ge-achc.txt:     compatible = "ge,achc";
Documentation/devicetree/bindings/misc/lwn-bk4.txt:- compatible : Should be "lwn,bk4"
Documentation/devicetree/bindings/misc/lwn-bk4.txt:     compatible = "lwn,bk4";

So, the shield could be hosting one of those say
 ge,achc or maybe lwn,bk4 ?- will probably be good to document the
dts is for such a configuration, though it is possible that such a
configuration might work for others?

I agree with Mark that "dt should indicate specific hardware" and we
should constraint the definition in such a scope?

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Are we talking about spidev here? Then let's drop that node, but I do
need to know how to describe spidev properly

yes - the spidev is my problem. can you drop the node and repost? i cant
locally modify and hope it works.

Done.

Thanks, I will try and pick up the v5 later today - need to redo my
sanity checkups.

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D