Re: [PATCH v2 00/13] i2c: add and start using i2c_adapter-specific printk helpers

Hi Bart, hi Johan,

And I agree: doing the above would be even better but you'd need - for every
driver - to move the i2c_adapter struct out of driver data and make it a
pointer. That's in addition to providing new APIs and using them. I2C drivers
are spread treewide. There's a reason why nobody attempted it for decades. I'm
proposing something a bit less complex: allow drivers to free i2c_adapter at
unbind but make i2c core keep a private, reference-counted structure for as
long as it's needed.

I am still with Bart, the above paragraph sums it up extremly well IMO.
I also recall that the outcome of the Plumbers session 2024 was "go for
it!". Nobody said the approach would be "fighting" the driver model.
There were a lot of experienced developers in the room.

I'm frustrated because I'm spending time working on an actual solution. I've
explained what I'm doing and what the end result will look like based on what
works for GPIO (struct gpio_chip's lifetime is bound to device's "bound" state,
struct gpio_device is refcounted, I want to mirror it with i2c_adapter and
whatever we eventually call its refcounted counterpart - let's say:
i2c_bus_device).

I am super-happy and thankful that Bart volunteers to spend all this
time on fixing this decade old problem. I know this alone is not a
reason to accept a technically bad solution. But I think it isn't. I
think it is a viable approach to keep the churn and potential
regressions lower than a theoretically ideal solution which is nobody to
do anyways because you'd need to refactor drivers from the 90s in a
quite intrusive way.

All the best,

   Wolfram