[REGRESSION] bcm2835-audio fails to register on vchiq-bus in monolithic kernels since 6.19 (VCHIQ destaging?)

[Martin Wetterwald]

I also tested current mainline (7.3-rc7), and I confirm the issue is
still there.
Martin

On Tue, Oct 13, 2026 at 9:28 AM Martin Wetterwald <martin at wetterwald.eu> wrote:
>
> Hi Jai, Thorsten,
>
> > Hmm, no answer, so it seems nobody really cares. A bisection might help.
> > Or at least validating your suspicion, hence: why can't you check the
> > parent of aa125180c6738 and aa125180c6738 itself? Or at least the range
> > with that commit in it? And is latest 7.3-rc still broken?
> >
> > Ciao, Thorsten
>
> Thanks Thorsten for the follow up!
> I didn't bisect because my image builder tool was not meant for kernel
> development: it could only download stable release tarballs signed by Greg.
>
> But now I've found a way around it and I've just bisected the issue! I've
> bisected through the 6523 revisions between 6.18 and 6.19-rc1.
>
> (The bisection was made on a Raspberry Pi 1B rev2 this time.)
>
> > aa125180c673881f88b528600b57865dc158b3a7 is the first 'bad' commit
> I confirm the issue was introduced by following commit:
>
> > commit aa125180c673881f88b528600b57865dc158b3a7
> > Author: Jai Luthra <jai.luthra at ideasonboard.com>
> > Date:   Wed Oct 29 16:00:10 2025 +0530
> >
> >     platform/raspberrypi: Destage VCHIQ interface
> >
> >     Destage the VCHIQ interface driver to drivers/platform/raspberrypi.
> >
> >     There is still the remaining TODO item of improving the documentation,
> >     which can be handled post destaging.
> >
> >     Secondly, multimedia drivers like codec and ISP that rely on this
> >     interface need to be upstreamed. And lastly, the drivers that facilitate
> >     the shared memory between VideoCore and Linux, like the vc-sm-cma driver
> >     and vc_mem char driver also need to be upstreamed.
> >
> >     Signed-off-by: Jai Luthra <jai.luthra at ideasonboard.com>
> >     Link: https://patch.msgid.link/20251029-vchiq-destage-v3-6-da8d6c83c2c5@ideasonboard.com
> >     Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
>
> #regzbot introduced: aa125180c673881f88b528600b57865dc158b3a7
>
> > Sorry, this got lost in my inbox last month. It's likely my series that
> > destaged VCHIQ broke the ordering as Martin suspects. I always tested with
> > modules enabled so didn't encounter this issue.
> >
> > I'll look into how we can ensure the VCHIQ bus gets registered before
> > peripheral drivers (like audio here) when CONFIG_MODULES=n. If someone
> > already knows what to do, pointers are appreciated :-)
>
> Thanks Jai!
> I'm willing to make the patch, but I'm not familiar with initialization order
> in the kernel boot sequence.
> Would also love if someone has pointers on good ways to influence order of boot
> sequence.
>
> Martin