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

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Message-ID: <87y1urpa9c.wl-maz@kernel.org>
Date:   Sat, 10 Sep 2022 15:35:59 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Frank Li <frank.li@....com>
Cc:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
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        Peng Fan <peng.fan@....com>,
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Subject: Re: [EXT] Re: [PATCH v9 2/4] irqchip: Add IMX MU MSI controller driver

On Fri, 09 Sep 2022 15:59:01 +0100,
Frank Li <frank.li@....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.