linux-kernel - Re: [PATCH 05/14] dt-bindings: trivial-devices: add GOcontroll Moduline IO modules

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Message-ID:
 <PA4PR04MB76306D77C93FF2C51524BD95C5C32@PA4PR04MB7630.eurprd04.prod.outlook.com>
Date: Tue, 25 Feb 2025 12:24:09 +0000
From: Maud Spierings | GOcontroll <maudspierings@...ontroll.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
CC: Rob Herring <robh@...nel.org>, Neil Armstrong <neil.armstrong@...aro.org>,
	Jessica Zhang <quic_jesszhan@...cinc.com>, Maarten Lankhorst
	<maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Thierry Reding
	<thierry.reding@...il.com>, Sam Ravnborg <sam@...nborg.org>, Liu Ying
	<victor.liu@....com>, Shawn Guo <shawnguo@...nel.org>, Sascha Hauer
	<s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 05/14] dt-bindings: trivial-devices: add GOcontroll
 Moduline IO modules

From: Krzysztof Kozlowski <krzk@...nel.org>
Sent: Tuesday, February 25, 2025 12:52 PM
 
>On Tue, Feb 25, 2025 at 07:39:52AM +0000, Maud Spierings | GOcontroll wrote:
>> From: Rob Herring <robh@...nel.org>
>> Sent: Monday, February 24, 2025 9:44 PM
>>  
>> >On Mon, Feb 24, 2025 at 02:50:55PM +0100, Maud Spierings wrote:
>> >> The main point of the Moduline series of embedded controllers is its
>> >> ecosystem of IO modules, these currently are operated through the spidev
>> >> interface. Ideally there will be a full dedicated driver in the future.
>> >>
>> >> Add the gocontroll moduline-module-slot device to enable the required
>> >> spidev interface.
>> >>
>> >> Signed-off-by: Maud Spierings <maudspierings@...ontroll.com>
>> >> ---
>> >>  Documentation/devicetree/bindings/trivial-devices.yaml | 2 ++
>> >>  1 file changed, 2 insertions(+)
>> >>
>> >> diff --git a/Documentation/devicetree/bindings/trivial-devices.yaml b/Documentation/devicetree/bindings/trivial-devices.yaml
>> >> index 8255bb590c0cc619d15b27dcbfd3aa85389c0a54..24ba810f91b73efdc615c7fb46f771a300926f05 100644
>> >> --- a/Documentation/devicetree/bindings/trivial-devices.yaml
>> >> +++ b/Documentation/devicetree/bindings/trivial-devices.yaml
>> >> @@ -107,6 +107,8 @@ properties:
>> >>            - fsl,mpl3115
>> >>              # MPR121: Proximity Capacitive Touch Sensor Controller
>> >>            - fsl,mpr121
>> >> +            # GOcontroll Moduline module slot for spi based IO modules
>> >
>> >I couldn't find anything about SPI for GOcontroll Moduline. Can you
>> >point me to what this hardware looks like. Based on what I did find,
>> >this seems incomplete and not likely a trivial device.
>>
>> I'll give some more details, if there is a v2 of this patch I will also
>> add more information in the commit message.
>>
>> The module slots have a number of pins, a lot of them currently unused as
>> they have not found a function yet, this is very much still a developing
>> product. The currently used interfaces to the SoC are:
>> 1. SPI bus as a spidev to ease developing new modules and quickly
>> integrate them. This is the main communication interface for control and
>> firmware updates.
>> 2. A reset pin, this is/was driven with the gpio-led driver but I doubt
>> that would get accepted upstream so I intend to switch to the much better
>> suited libgpio.
>
>reset-gpios is not in trivial devices, so that's already a hint you
>cannot use this binding.
>
>> 3. An interrupt pin, this is currently only used in the firmware update
>> utility [2] to speed up the update process. Other communication is done at
>> a regular interval.
>>
>> What is unused:
>> 1. A potentially multi-master i2c bus between all the module slots and
>> the SoC
>> 2. An SMBus alert line is shared between the modules, but not the SoC.
>> 3. A shared line designated as a clock line, intended to in the future
>> aid with synchronizing modules to each other for time critical control.
>>
>> current software that is used to work with the modules can be found at
>> [2] and [3], one of them is a Node-RED module the other is a blockset for
>> Matlab/Simulink generated code.
>>
>> If you know a better way I could describe this in the devicetree then I
>
>You need dedicated binding where you describe entire device, entire
>hardware, not what your driver supports in current release.

I see now that I also forgot the patch that adds this compatible to the
spidev driver. Didn't check for the spidevs in testing I guess.

Could I write bindings for this device, and then add the compatible to the
spidev driver for now? So it probes that driver, and then later when there
is a driver remove the compatible there and keep it only in the purpose
built driver?

So I'll write gocontroll,moduline-module-slot.yaml, don't quite know where
that would go. Define all these attributes in there and then add the 
compatible to drivers/spi/spidev.c

Is that okay?

Kind regards,
Maud