linux-kernel - Re: [PATCH 00/11] arm/arm64: Turning IPIs into normal interrupts

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Message-ID: <20200612104918.3829bb26@why>
Date:   Fri, 12 Jun 2020 10:49:18 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Sumit Garg <sumit.garg@...aro.org>, kernel-team@...roid.com,
        Russell King <linux@....linux.org.uk>,
        Jason Cooper <jason@...edaemon.net>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH 00/11] arm/arm64: Turning IPIs into normal interrupts

Hi Florian,

On Tue, 19 May 2020 10:50:46 -0700
Florian Fainelli <f.fainelli@...il.com> wrote:

> On 5/19/2020 9:17 AM, Marc Zyngier wrote:
> > For as long as SMP ARM has existed, IPIs have been handled as
> > something special. The arch code and the interrupt controller exchange
> > a couple of hooks (one to generate an IPI, another to handle it).
> > 
> > Although this is perfectly manageable, it prevents the use of features
> > that we could use if IPIs were Linux IRQs (such as pseudo-NMIs). It
> > also means that each interrupt controller driver has to follow an
> > architecture-specific interface instead of just implementing the base
> > irqchip functionnalities. The arch code also duplicates a number of
> > things that the core irq code already does (such as calling
> > set_irq_regs(), irq_enter()...).
> > 
> > This series tries to remedy this on arm/arm64 by offering a new
> > registration interface where the irqchip gives the arch code a range
> > of interrupts to use for IPIs. The arch code requests these as normal
> > interrupts.
> > 
> > The bulk of the work is at the interrupt controller level, where all 3
> > irqchips used on arm64 get converted.
> > 
> > Finally, the arm64 code drops the legacy registration interface. The
> > same thing could be done on 32bit as well once the two remaining
> > irqchips using that interface get converted.
> > 
> > There is probably more that could be done: statistics are still
> > architecture-private code, for example, and no attempt is made to
> > solve that (apart from hidding the IRQs from /proc/interrupt).
> > 
> > This has been tested on a bunch of 32 and 64bit guests.  
> 
> Does this patch series change your position on this patch series
> 
> https://lore.kernel.org/linux-arm-kernel/20191023000547.7831-3-f.fainelli@gmail.com/T/
> 
> or is this still a no-no?

I don't think this series changes anything. There is no easy way to
reserve SGIs in a way that would work for all combination of OS and FW,
and the prospect of sending SGIs between S and NS has already been
dubious (yes, the GIC architecture allows it, but it has been written
by people who have never designed any large piece of SW).

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...