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

[Ayush Singh]

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