linux-kernel - Re: [PATCH 3/6] irqchip: RISC-V Local Interrupt Controller Driver

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Date:   Wed, 25 Jul 2018 13:24:57 +0200
From:   Christoph Hellwig <hch@....de>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Christoph Hellwig <hch@....de>, tglx@...utronix.de,
        palmer@...ive.com, jason@...edaemon.net, robh+dt@...nel.org,
        mark.rutland@....com, devicetree@...r.kernel.org,
        aou@...s.berkeley.edu, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, shorne@...il.com,
        Palmer Dabbelt <palmer@...belt.com>
Subject: Re: [PATCH 3/6] irqchip: RISC-V Local Interrupt Controller Driver

On Wed, Jul 25, 2018 at 12:18:39PM +0100, Marc Zyngier wrote:
> This feels odd. It means that you cannot have the following sequence:
> 
> 	local_irq_disable();
> 	enable_irq(x); // where x is owned by a remote hart
> 
> as smp_call_function_single() requires interrupts to be enabled.
> 
> More fundamentally, why are you trying to make these interrupts look
> global while they aren't? arm/arm64 have similar restrictions with GICv2
> and earlier, and treats these interrupts as per-cpu.
> 
> Given that the drivers that deal with drivers connected to the per-hart
> irqchip are themselves likely to be aware of the per-cpu aspect, it
> would make sense to align things (we've been through that same
> discussion about the clocksource driver a few weeks back).

Right now the only direct consumers are said clocksource, the PLIC
driver later in this series and the RISC-V arch IPI code.  None of them
is going to do a manual enable_irq, so I guess the remote case of the
code is simply dead code.  I'll take a look at converting them to
per-cpu.  I guess the GICv2 driver is the best template?