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

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Message-ID: <CAAhSdy31=D3jOgvrc+Td-TeKQMazPA-suFjOy9XwEuima1WdeA@mail.gmail.com>
Date:   Thu, 26 Jul 2018 09:08:00 +0530
From:   Anup Patel <anup@...infault.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Thomas Gleixner <tglx@...utronix.de>, palmer@...ive.com,
        jason@...edaemon.net, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, aou@...s.berkeley.edu,
        "linux-kernel@...r.kernel.org List" <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 4:54 PM, Christoph Hellwig <hch@....de> 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?

Actually, RISCV HLIC and PLIC are very similar to RPi2 and RPi3 SOCs.

On RPi2 and RPi3, we have per-CPU BCM2836 local intc and the global
interrupts are managed using BCM2835 intc. You should certainly have
a look a this drivers because these very simple compared to GICv2 and
GICv3 drivers.

Regards,
Anup