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Date:   Thu, 11 Mar 2021 11:56:58 -0600
From:   Nishanth Menon <nm@ti.com>
To:     Jan Kiszka <jan.kiszka@siemens.com>
CC:     Tero Kristo <kristo@kernel.org>, Rob Herring <robh+dt@kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <devicetree@vger.kernel.org>,
        Le Jin <le.jin@siemens.com>,
        Bao Cheng Su <baocheng.su@siemens.com>,
        Vignesh Raghavendra <vigneshr@ti.com>
Subject: Re: [PATCH v4 3/3] arm64: dts: ti: Add support for Siemens IOT2050
 boards
Message-ID: <20210311175658.agmnphz2pjydwnc5@annex>
References: <cover.1615369068.git.jan.kiszka@siemens.com>
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 <20210311131754.i5ewls6hgeitcgre@astonish>
 <8d076ff1-cdac-941f-e796-a2e6dba792ab@siemens.com>
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On 15:36-20210311, Jan Kiszka wrote:
> On 11.03.21 15:21, Nishanth Menon wrote:
> > On 15:14-20210311, Jan Kiszka wrote:
> > 
> > [...]
> > 
> >>>
> >>> 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?

[...]

> > 
> >> 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