Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sat, Mar 14, 2026 at 11:42:02AM +0000, Markus Probst wrote:
> On Sat, 2026-03-14 at 09:07 +0100, Greg Kroah-Hartman wrote:
> > On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote:
> > > Add rust private data to `struct serdev_device`, as it is required by the
> > > rust abstraction added in the following commit
> > > (rust: add basic serial device bus abstractions).
> > 
> > why is rust "special" here?  What's wrong with the existing private
> > pointer in this structure?  Why must we add another one?
> Because in rust, the device drvdata will be set after probe has run. In
> serdev, once the device has been opened, it can receive data. It must
> be opened either inside probe or before probe, because it can only be
> configured (baudrate, flow control etc.) and data written to after it
> has been opened. Because it can receive data before drvdata has been
> set yet, we need to ensure it waits on data receival for the probe to
> be finished. Otherwise this would be a null pointer dereference. To do
> this, we need to store a `Completion` for it to wait and a `bool` in
> case the probe exits with an error. We cannot store this data in the
> device drvdata, because this is where the drivers drvdata goes. We also
> cannot create a wrapper of the drivers drvdata, because
> `Device::drvdata::<T>()` would always fail in that case. That is why we
> need a "rust_private_data" for this abstraction to store the
> `Completion` and `bool`.

So why is this any different from any other bus type?  I don't see the
"uniqueness" here that has not required this to happen for PCI or USB or
anything else.

What am I missing?

Also, all of this information MUST be in the changelog text in order for
us to be able to accept it.  You need to say _why_ a change is needed,
not just _what_ the change does, as you know.

thanks,

greg k-h