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

[Alice Ryhl <aliceryhl@google.com>]

On Sat, Mar 14, 2026 at 12:08:09PM +0000, Markus Probst wrote:
> On Sat, 2026-03-14 at 12:52 +0100, Greg Kroah-Hartman wrote:
> > 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?
> In Short:
> In serdev, we have to handle incoming device data (serdev calls on a
> function pointer we provide in advance), even in the case that the
> driver hasn't completed probe yet.

Why can the function pointers be called during probe?

Alice