linux-kernel - Re: [EXT] Re: [PATCH 1/2 v4] dt-bindings: dspi: added for semtech sx1301

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Date:   Thu, 21 Apr 2022 11:44:21 +0200
From:   Michael Walle <michael@...le.cc>
To:     krzysztof.kozlowski@...aro.org
Cc:     broonie@...nel.org, devicetree@...r.kernel.org,
        jerry.huang@....com, krzysztof.kozlowski+dt@...aro.org,
        leoyang.li@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
        robh+dt@...nel.org, shawnguo@...nel.org,
        Vladimir Oltean <olteanv@...il.com>,
        Michael Walle <michael@...le.cc>
Subject: Re: [EXT] Re: [PATCH 1/2 v4] dt-bindings: dspi: added for semtech sx1301

On 21/04/2022 11:11, Jerry Huang wrote:
>> Please also answer Michael's comments.
>> 
>> [Jerry Huang] I double checked the MikroBus devices, we used two MikcroBus devices:
>> BLE P click: https://www.mikroe.com/ble-p-click
>> BEE click: https://www.mikroe.com/bee-click 
>> Both of them are SPI interface connect to ls1028ardb through MiKcroBus interface.
>> So the name "semtech sx1301" is not correct for this node.
>
> I asked to remove the words "Devicetree bindings" and this was not finished.
> 
> Now you mention that entire name of device is wrong... It's confusing. I
> don't know what device you are describing here. I expect you know. :)
> 
> What is this binding about exactly?

I *think* it's just exposing the mikrobus connector as an spidev device.
There was a former attempt by Vladimir here [1]. Now as it the nature
of such a connector that you can connect a myriad of devices there, it
doesn't really make sense to have a just particular one described. What
happens if that one will switch from spidev to a real driver in the
kernel? So using "spidev" for the compatible would be the first reflex.
But as described in the spidev driver this is plain wrong (and also causes
a warning/info message it) because it should describe the actual hardware.

Thus I proposed to use DT overlays which are loaded according to what
is actually attached to the header, so a real driver could be loaded.

But there *could* be a sane default which then could be replaced in
an DT overlay. Like "mirkobus-socket" or similar, which might expose
spidev. Actually it is more than just SPI, there is GPIO and resets and
I2C. Maybe it should be an MFD? I don't know. But that is something for
the DT maintainers to decide if they'll allow such "generic" devices.

-michael

[1] https://lore.kernel.org/linux-devicetree/20200318001603.9650-13-olteanv@gmail.com/