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

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Message-ID: <2025050426-expel-overarch-3454@gregkh>
Date: Sun, 4 May 2025 15:13:01 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Ayush Singh <ayush@...gleboard.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 Sun, May 04, 2025 at 06:30:24PM +0530, Ayush Singh wrote:
> 
> 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.

uarts are not a bus, they are a type of device that is implemented by
many different bus drivers (pci, USB, etc.)

thanks,

greg k-h