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

[Markus Probst]

On Fri, 2026-03-20 at 20:59 +0100, Danilo Krummrich wrote:
> On 3/20/26 6:13 PM, Markus Probst wrote:
> > This is unique for a bus device.
> > 
> > A class device has its own Data (e. g. PwmOps), i. e. it will only be
> > registered after this Data has been initialized by the driver.
> > 
> > The receive_buf callback on the serdev device on the other hand must
> > happen on the drvdata, as there is no place to store its own Data.
> > 
> > The drvdata is only available at the end of the probe in Rust.
> 
> In other words, devm_serdev_device_open() relies on the driver having its
> private data set before this is called, since once devm_serdev_device_open() has
> been called, the driver's receive_buf() callback may be called.
> 
> So, in C it is the driver's responsibility to do things in the correct order, in
> Rust we want to make sure the driver can't do it out of order in the first place.
> 
> I'm still not sure whether the current approach is the best option. For
> instance, we could also solve this with a separate callback.
> 

> Wasn't this even
> what you had in a previous version?
Yes, but Kari pointed out that changing the ops while it is in use is
unsafe [1].

Thanks
- Markus Probst

[1]
https://lore.kernel.org/rust-for-linux/CAC=eVgR2WYdDTW3kOeemyQPP-H0aAUsrzn5Gk5zCe2hQEB709w@xxxxxxxxxxxxxx/

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