linux-kernel - Re: exporting a device type

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Message-ID: <CAHp75Vff+at=Ty0GD1PpROPJqHEAB+g94pv-CLbeT2aTN46uJw@mail.gmail.com>
Date: Sat, 12 Apr 2025 20:56:39 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: exporting a device type

On Sat, Apr 12, 2025 at 12:25 AM Danilo Krummrich <dakr@...nel.org> wrote:
> On Fri, Apr 11, 2025 at 10:39:38PM +0300, Andy Shevchenko wrote:
> > I have an issue with this change
> >
> > https://web.git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/commit/?h=for-driver-core&id=e86cc69186051d7312711565803de586efd9b2cf
> >
> > (I think you haven't yet sent it for review, so this is just
> > preliminary look at)
> >
> > The idea of exporting bus type will open a non-reversible box of
> > changes when people will start abusing it. Instead just provide an API
> > dev_is_auxiliary() as it's done in other subsystems (yes, I know that
> > some of them are still exporting the type, but it's most likely due to
> > historical reasons of not thinking through it at that time).
>
> Yeah, most busses export it and provide a dev_is_*() macro, which we can't use
> in Rust. That's why for PCI and platform I started using the bus type directly,
> see e.g. [1].

I know. When I tried to do the same for PNP devices, Greg and others
were objecting to this. An auxiliary bus is a new thing and I don't
believe that Greg or any other kernel developer who is generally in
favour of Rust development will accept this particular change.

> However, I already considered changing it up by just creating Rust helper
> functions for the dev_is_*() macros and provide a dev_is_auxiliary() API
> instead. This also simplifies things a bit and gets me rid of the
> Device::bus_type_raw() helper.

This would be wonderful!

> [1] https://web.git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/commit/?h=for-driver-core&id=d72c42c1da4149fec28e3b180654bf5fd88c2094



-- 
With Best Regards,
Andy Shevchenko