Re: RE: Re:RE: [PATCH] pinctrl: mcp23s08: reject devices without match data

[Linus Walleij]

On Fri, Oct 2, 2026 at 12:19 PM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> On Fri, Oct 02, 2026 at 11:52:41AM +0200, Linus Walleij wrote:
> > On Fri, Oct 2, 2026 at 8:59 AM Andy Shevchenko

> > The entire name of the thing feels like debugfs-footgun
> > territory for example.
>
> Yeah, I can't find neither a thing on LWN.net nor in the in-tree documentation.
> The only useful piece of information is (in kernel-doc of struct bus_type):
>
>   driver_override
>     Set to true if this bus supports the driver_override mechanism, which
>     allows userspace to force a specific driver to bind to a device via a sysfs
>     attribute.

This whole thing is weird, but OK.

Since we have a ton of drivers depending on match data we either
have to patch them all to bail out if match data is NULL (like this
patch does) or, which is equivalent, opt out of driver_override
that much is certain.

What I don't get is what this is intended for. What is the use case?
The commit says this is for VFIO. Shouldn't it be opt-in and turned
on only for VFIO then?

Kim Phillips is listed as contract for the platform bus driver_override
so let's ask! Kim: what is this for?

All of the device tree drivers use the platform bus, what's yhe
Unique Selling Point of this for our devices?

Yours,
Linus Walleij