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

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Message-ID: <VE1PR04MB6477AC00BF08A787EBF433F3FEF49@VE1PR04MB6477.eurprd04.prod.outlook.com>
Date:   Thu, 21 Apr 2022 10:06:17 +0000
From:   Jerry Huang <jerry.huang@....com>
To:     Michael Walle <michael@...le.cc>,
        "krzysztof.kozlowski@...aro.org" <krzysztof.kozlowski@...aro.org>
CC:     "broonie@...nel.org" <broonie@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>, Leo Li <leoyang.li@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "shawnguo@...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




Best Regards
Jerry Huang

-----Original Message-----
From: Michael Walle <michael@...le.cc> 
Sent: 2022年4月21日 17:44
To: krzysztof.kozlowski@...aro.org
Cc: broonie@...nel.org; devicetree@...r.kernel.org; Jerry Huang <jerry.huang@....com>; krzysztof.kozlowski+dt@...aro.org; Leo Li <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

Caution: EXT Email

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://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww
>> .mikroe.com%2Fble-p-click&amp;data=05%7C01%7Cjerry.huang%40nxp.com%7C
>> 39106c035c374b5ec60608da237b883f%7C686ea1d3bc2b4c6fa92cd99c5c301635%7
>> C0%7C1%7C637861310738684479%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM
>> DAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000%7C%7C%7C&amp
>> ;sdata=rsETzlFhfe2hyRAiQOL4KHAQ4vwh%2FFrYzroZ%2B0ccSMw%3D&amp;reserve
>> d=0 BEE click: 
>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww
>> .mikroe.com%2Fbee-click&amp;data=05%7C01%7Cjerry.huang%40nxp.com%7C39
>> 106c035c374b5ec60608da237b883f%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0
>> %7C1%7C637861310738684479%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDA
>> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000%7C%7C%7C&amp;s
>> data=LEmwF46B9GYD%2BcpGoxpiGTnMgvTbLHP4IUirGR78A5U%3D&amp;reserved=0
>> 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

[Jerry Huang] 
Thank a lot, Michael.
Yes, there are I2C, Uart (or GPIO) and SPI interface in MikcroBus socket. 

Krzysztof,
How about 
compatible = "mikcroe,mikcroe-socket"?
or how about Vladimir's patch?



[1] https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flinux-devicetree%2F20200318001603.9650-13-olteanv%40gmail.com%2F&amp;data=05%7C01%7Cjerry.huang%40nxp.com%7C39106c035c374b5ec60608da237b883f%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C1%7C637861310738684479%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000%7C%7C%7C&amp;sdata=Y166YDGSpEX0wtUQE8V7ql8atkb79BmG9Y5mXb8KWJM%3D&amp;reserved=0