Re: Question about the maintenance of OOT RT patches for LTS releases (v12.x and v18.x)

["Luis Claudio R. Goncalves" <lgoncalv@redhat.com>]

On Wed, Jun 24, 2026 at 08:49:44AM +0200, Sebastian Andrzej Siewior wrote:
> On 2026-06-22 13:11:59 [-0300], Luis Claudio R. Goncalves wrote:
> > Hello!
> > 
> > The question is simple:
> > 
> >    Should we have somebody maintaining the OOT RT patches for v12.x and v18.x,
> >    the LTS versions that already have PREEMPT_RT in-tree?
> > 
> > As we still have a few OOT patches, after a while, people using PREEMPT_RT on
> > those versions may encounter conflicts trying to apply the old patches. And
> > as those patches are not in-tree, the fixes won't probably be routed via
> > Stable.
> 
> For 6.18, we have:
> - 8250 console
> - i915
> - arm-32
> - powerpc
> 
> For 6.12, we have additionally
> - ktimers thread
> - the whole lazy-preempt

I need to correct myself here, our local hero Daniel Wagner is maintaining
the v6.12-rt version. Sorry for that :)

Sebastian, just to make sure I understood your answer, then we don't need
to keep the OOT patches up-to-date for v6.18-rt specifically? My question
came from comments raised on the last two RT maintainers meetings and the
LF RT Board meeting. I just want to have a good answer if somebody else
asks about that. And to volunteer if work is needed.

Best,
Luis
 
> So for v6.12 there are bits outstanding which can impact you.
> For v6.18 if you are on arm64 then the mainline version is slightly
> better than on x86 because on arm64 you might be using the pl011 UART
> which has nbcon support since v6.15 while on x86 you almost always have
> the 8250 which is not yet with nbcon support in-tree.
> 
> These are the missing bits. None of them are essential. If you on x86
> and your kernel crashes, it is more likely to see a backtrace with nbcon
> driver than without it.
> 
> > Best regards,
> > Luis
> 
> Sebastian
> 
---end quoted text---