Re: [PATCH 0/8] Device: generic accessors for drvdata + Driver::unbind()

[Danilo Krummrich <dakr@kernel.org>]

On Mon, Jul 07, 2025 at 04:18:09PM +0900, Alexandre Courbot wrote:
> On Tue Jul 1, 2025 at 7:40 PM JST, Danilo Krummrich wrote:
> >> > This makes it inefficient (but not impossible) to access device
> >> > resources, e.g. to write device registers, and impossible to call device
> >> > methods, which are only accessible under the Core device context.
> >> > 
> >> > In order to solve this, add an additional callback for (1), which we
> >> > call unbind().
> >> > 
> >> > The reason for calling it unbind() is that, unlike remove(), it is *only*
> >> > meant to be used to perform teardown operations on the device (1), but
> >> > *not* to release resources (2).
> >> 
> >> Ick.  I get the idea, but unbind() is going to get confusing fast.
> >> Determining what is, and is not, a "resource" is going to be hard over
> >> time.  In fact, how would you define it?  :)
> >
> > I think the definition is simple: All teardown operations a driver needs a
> > &Device<Core> for go into unbind().
> >
> > Whereas drop() really only is the destructor of the driver's private data.
> >
> >> Is "teardown" only allowed to write to resources, but not free them?
> >
> > "Teardown" is everything that involves interaction with the device when the
> > driver is unbound.
> >
> > However, we can't free things there, that happens in the automatically when the
> > destructor of the driver's private data is called, i.e. in drop().
> 
> Can't we somehow make a (renamed) `unbind` receive full ownership of the
> driver's private data, such that it will be freed (and its `drop`
> implementation called) before `unbind` returns? Or do we necessarily
> need to free that data later?

No, we could do that. And I thought about this as well, but I really want to
bind the lifetime of the driver's private data stored in a device to the
lifetime of this driver being bound to the device.

I don't think there is a valid use-case to allow this data as a whole to
out-live driver unbind arbitrarily.