linux-kernel - Re: [Discussion] Global vs Local devicetree overlays for addon board + connector setups

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Message-ID: <eefa06c1-478f-4670-80c7-4bde8c808e1b@beagleboard.org>
Date: Sun, 4 May 2025 18:30:24 +0530
From: Ayush Singh <ayush@...gleboard.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Herve Codina <herve.codina@...tlin.com>, xypron.glpk@....de,
 Jason Kridner <jkridner@...gleboard.org>,
 Deepak Khatri <lorforlinux@...gleboard.org>, Dhruva Gole <d-gole@...com>,
 Robert Nelson <robertcnelson@...gleboard.org>, Andrew Davis <afd@...com>,
 Geert Uytterhoeven <geert@...ux-m68k.org>,
 David Gibson <david@...son.dropbear.id.au>,
 Luca Ceresoli <luca.ceresoli@...tlin.com>,
 Pantelis Antoniou <pantelis.antoniou@...il.com>,
 "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
 <devicetree@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [Discussion] Global vs Local devicetree overlays for addon board
 + connector setups


On 5/4/25 18:20, Greg Kroah-Hartman wrote:
> On Sun, May 04, 2025 at 06:03:26PM +0530, Ayush Singh wrote:
>>> It depends on the bus the device is added.
>>> when an overlay is applied by the kernel, OF_RECONFIG_* events are
>>> triggered. Some buses handle them:
>>>
>>> 	$ git grep OF_RECONFIG_CHANGE
>>> 	drivers/bus/imx-weim.c: case OF_RECONFIG_CHANGE_ADD:
>>> 	drivers/bus/imx-weim.c: case OF_RECONFIG_CHANGE_REMOVE:
>>> 	drivers/gpio/gpiolib-of.c:      case OF_RECONFIG_CHANGE_ADD:
>>> 	drivers/gpio/gpiolib-of.c:      case OF_RECONFIG_CHANGE_REMOVE:
>>> 	drivers/i2c/i2c-core-of.c:      case OF_RECONFIG_CHANGE_ADD:
>>> 	drivers/i2c/i2c-core-of.c:      case OF_RECONFIG_CHANGE_REMOVE:
>>> 	drivers/of/dynamic.c: * Return: OF_RECONFIG_CHANGE_REMOVE on device going from enabled to
>>> 	drivers/of/dynamic.c: * disabled, OF_RECONFIG_CHANGE_ADD on device going from disabled to
>>> 	drivers/of/dynamic.c:   return new_state ? OF_RECONFIG_CHANGE_ADD : OF_RECONFIG_CHANGE_REMOVE;
>>> 	drivers/of/platform.c:  case OF_RECONFIG_CHANGE_ADD:
>>> 	drivers/of/platform.c:  case OF_RECONFIG_CHANGE_REMOVE:
>>> 	drivers/spi/spi.c:      case OF_RECONFIG_CHANGE_ADD:
>>> 	drivers/spi/spi.c:      case OF_RECONFIG_CHANGE_REMOVE:
>>> 	include/linux/of.h:     OF_RECONFIG_CHANGE_ADD,
>>> 	include/linux/of.h:     OF_RECONFIG_CHANGE_REMOVE,
>>
>> Well, if some bus does handle the event, I guess it is a bug in the
>> subsystems that do not? Maybe Greg Kroah-Hartman can clarify the expected
>> behavior here? Maybe we are in transition phase here.
> Perhaps those other busses just do not have OF devices and so they never
> needed to add that functionality to them?
>
> If they do, then by all means add that code.  OF devices are not
> possible for many bus types, so there shouldn't be a need to add this to
> the driver core, right?
>
> thanks,
>
> greg k-h


UART devices are pretty common in both Beagle capes and MikroBUS. So I 
think that will probably need to be added at some point.


Ayush Singh