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

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Message-ID: <663d9e81-9036-6986-f52a-3846b4b5c673@linaro.org>
Date:   Thu, 21 Apr 2022 13:08:28 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Michael Walle <michael@...le.cc>
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>
Subject: Re: [EXT] Re: [PATCH 1/2 v4] dt-bindings: dspi: added for semtech
 sx1301

On 21/04/2022 11:44, Michael Walle wrote:
> 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]. 

That explains a lot, thanks! It's a pity it was not described here.

> 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.

spidev device nodes are in general allowed, using the specific
compatible for a real device attached to the SPI.

Here it seems clearly that it's not the case. Using roghm,dh2228fv as a
"spidev" compatible for something else was wrong.

Adding another device - sx1301 - also does not look correct, if it is
not there.

> 
> 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.

I think if you have DT overlay, you can add device node and there is no
need for placeholder, right?

Best regards,
Krzysztof