Re: [PATCH v4 1/5] dt-bindings: misc: Add mikrobus-connector

Andrew Lunn
2024-03-22T18:51:31Z

> After going through all the discussions here, I have a few questions:
>
> 1. Is the old `*_register_device(controller, board_info)` style discouraged
> in favor of using device tree, at least for drivers using multiple
> fundamental buses (i2c, spi, etc)?

Historically, they were used in board files, where you needed to write
C code for every single board. That did not scale, which is why we
swapped to DT.

board_info is still useful, e.g. for platforms which don't have DT. I
support a few amd64 boards where i need to use a platform driver to
instantiate some I2C and MDIO devices. But in general DT is much
easier to use.

> 2. Is the preferred way to handle virtual devices (like those created by
> greybus subsystem) now device tree? Is that one of the blockers for greybus
> i2c, spi etc to still be in staging?

I would not say they are virtual. They do exist. They are just not
memory mapped like most devices, but in another address space, one
which you access via RPCs.

>
> 3. How are virtual devices created in device tree? If I register an i2c
> adapter using `i2c_add_adapter`, is the device tree entry is dynamically
> created, which can then be used by a device tree overlay?

As far as i'm aware, there are no examples today. You are doing
something different, something new. Adding these dynamic devices to DT
is just a suggestion from me, as a good way to solve your problem. You
will need to look into the DT core and figure out how to do it.

Andrew