Re: [EXT] Re: [PATCH v9 2/4] irqchip: Add IMX MU MSI controller driver

Marc Zyngier
2022-09-10T14:36:02Z

On Fri, 09 Sep 2022 15:59:01 +0100,
Frank Li <frank.li@nxp.com> wrote:
>
> > >
> > > [Frank Li] According to my understand, raw_spinlock skip some lockdep
> > > /debug feature to get better performance, which should be used when
> > > Frequently call, such as irq handle\polling thread.
> >
> > I'm afraid you are terribly misguided. They both have the same debug
> > features because they are both using the same core implementation, and
> > the only difference is whether this is preemptible for RT purposes or
> > not.
> >
> > > Spinlock have DEBUG feature to check wrong use lock. Allocate MSI
> > generally
> > > only is call once when driver probe.
> >
> > Again, you should really read the code and the documentation and stop
> > making things up.
>
> [Frank Li] Thanks. You give me the correct direction. Some stackoverflow's
> Doc was misleaded. I double checked spin_lock implementation. PREEMPT_RT
> Kernel map spin_lock to rt_mutex.
>
> I am curious why exist spin_lock_irqsave and raw_spin_lock_irqsave before
> PREEMTP_RT merge into kernel tree.

Because the RT merge has been going on for 10 years or so, long before
CONFIG_RT was merged. Also, a mutex has a spin lock at its core, and
it makes sense to have a single primitive for all these lock types.

M.

--
Without deviation from the norm, progress is not possible.