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

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Message-ID: <YmFo+EntwxIsco/t@robh.at.kernel.org>
Date:   Thu, 21 Apr 2022 09:23:52 -0500
From:   Rob Herring <robh@...nel.org>
To:     Michael Walle <michael@...le.cc>
Cc:     krzysztof.kozlowski@...aro.org, 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, shawnguo@...nel.org,
        Vladimir Oltean <olteanv@...il.com>
Subject: Re: [EXT] Re: [PATCH 1/2 v4] dt-bindings: dspi: added for semtech
 sx1301

On Thu, Apr 21, 2022 at 11:44:21AM +0200, 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]. 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.

generic devices, no. MFD, no. 

What's needed here is a connector node (and driver) for the mikrobus 
socket. The connector node's purpose is to decouple the host DT from 
add-on board overlay DT. Something like this:

connector {
	// And a more specific compatible if pins can have alt funcs?
	// Spec version needed?
	compatible = "mikrobus-socket"; 

	// Will need regulators defined if child devices expect 
	// regulators
	vcc-33-supply = <&reg33>;
	vcc-5-supply = <&reg5v>;

	i2c-parent = <&i2c1>; // Already a defined property
	spi-parent = <&spi0>; // New

	// RST pin
	reset-gpios = <&gpio 4 0>;
	
	// remap 'INT' (index 0) to host interrupt
	#interrupt-cells = <2>;
	#address-cells = <0>;
	interrupt-map = <0 0 &gpio 3 0>;

	spi {
		//devices
	};

	i2c {

	};
};

The DT spec defines 'foo-map' properties extending interrupt-map. 
Currently only GPIO is defined. We might want to do the same thing for 
PWM. Or we make the connector node both a PWM consumer and provider.

Rob