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

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Date:   Wed, 25 Jul 2018 12:37:11 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     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 25/07/18 12:24, Christoph Hellwig wrote:
> 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?

I think you can do a much better job than the GICv2 driver ;-). You have
the chance of a clean slate, and no legacy (or ACPI) junk to deal with!

I think this is just a matter of moving the HLIC declaration in DT to be
outside of the cpu nodes (you just have a single HLIC node that is valid
for all the CPUs in the system), and making the interrupts percpu_devid
in your mapping function (see gic_irq_domain_map for reference).

Thanks,

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