From: Anup Patel <anup@brainfault.org>
To: Marc Zyngier <maz@kernel.org>
Cc: Anup Patel <anup.patel@wdc.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Jason Cooper <jason@lakedaemon.net>,
Atish Patra <atish.patra@wdc.com>,
Alistair Francis <Alistair.Francis@wdc.com>,
linux-riscv <linux-riscv@lists.infradead.org>,
"linux-kernel@vger.kernel.org List"
<linux-kernel@vger.kernel.org>,
Palmer Dabbelt <palmerdabbelt@google.com>
Subject: Re: [PATCH v6 3/6] irqchip: RISC-V per-HART local interrupt controller driver
Date: Mon, 1 Jun 2020 09:39:16 +0530 [thread overview]
Message-ID: <CAAhSdy3-dr1URn1mGu3n9D-h+wjsU18nbWPYMRNAtitMa58rwA@mail.gmail.com> (raw)
In-Reply-To: <e315f76b06b7b0935ebee867c04f364e@kernel.org>
On Sun, May 31, 2020 at 4:23 PM Marc Zyngier <maz@kernel.org> wrote:
>
> On 2020-05-31 11:06, Anup Patel wrote:
> > On Sun, May 31, 2020 at 3:03 PM Marc Zyngier <maz@kernel.org> wrote:
> >>
> >> On 2020-05-31 06:36, Anup Patel wrote:
> >> > On Sat, May 30, 2020 at 5:31 PM Marc Zyngier <maz@kernel.org> wrote:
> >>
> >> [...]
> >>
> >> >> > plic_set_threshold(handler, PLIC_DISABLE_THRESHOLD);
> >> >>
> >> >> Why do you need to both disable the interrupt *and* change the
> >> >> priority
> >> >> threshold? It seems to be that one of them should be enough, but my
> >> >> kno9wledge of the PLIC is limited. In any case, this would deserve a
> >> >> comment.
> >> >
> >> > Okay, I will test and remove "disable the interrupt" part from
> >> > plic_dying_cpu().
> >>
> >> Be careful, as interrupt enabling/disabling is refcounted in order
> >> to allow nesting. If you only enable on CPU_ON and not disable
> >> on CPU_OFF, you will end-up with a depth that only increases,
> >> up to the point where you hit the roof (it will take a while though).
> >>
> >> I would keep the enable/disable as is, and drop the priority
> >> setting from the CPU_OFF path.
> >
> > The PLIC threshold is like GICv2 CPU interface enable/disable.
>
> Looking at the documentation[1], that's not really a correct analogy:
>
> - The PLIC is far removed from the CPU, and is more akin a GICv3
> distributor. The INTC itself is more like a GICv3 redistributor,
> as it deals with local interrupts only. I don't see anything
> in the RISC-V architecture that actually behaves like a GIC
> CPU interface (not necessarily a bad thing...).
>
> - The threshold register is not an ON/OFF, but a priority mask,
> similar to the GIC PMR (except that the PMR lives in the CPU
> interface and affects all interrupts targetting this CPU while
> this only seem to affect PLIC interrupts and not the INTC interrupts).
> You may be using it as an ON/OFF for now as you don't support
> multiple priorities yet, but that's just a SW thing.
Yes, your analogy is correct.
BTW, PLIC does not handle MSI and does not have virtualization support
pass-through interrupts. We will most likely see a new RISC-V interrupt
controller spec for these capabilities.
Also, the PLIC spec is now owned by RISC-V foundation (not SiFive) so
we will have to rename the driver to "irq-riscv-plic" and will have a new
generic compatible string "riscv,plic-1.0.0". One of us (me or Palmer) will
send separate patches for this renaming. I hope you will be fine with this??
(Refer, https://github.com/riscv/riscv-plic-spec)
>
> > Based on your comment, we should only program the PLIC threshold
> > in CPU_ON and don't touch the PLIC threshold in CPU_OFF. Right??
>
> This seems like the correct thing to do.
Sure, I will update.
>
> M.
>
> [1]
> https://sifive.cdn.prismic.io/sifive%2Fdc4980ff-17db-448b-b521-4c7ab26b7488_sifive+u54-mc+manual+v19.08.pdf
> --
> Jazz is not dead. It just smells funny...
Regards,
Anup
next prev parent reply other threads:[~2020-06-01 4:09 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-30 10:07 [PATCH v6 0/6] New RISC-V Local Interrupt Controller Driver Anup Patel
2020-05-30 10:07 ` [PATCH v6 1/6] RISC-V: self-contained IPI handling routine Anup Patel
2020-05-30 10:07 ` [PATCH v6 2/6] RISC-V: Rename and move plic_find_hart_id() to arch directory Anup Patel
2020-05-30 10:07 ` [PATCH v6 3/6] irqchip: RISC-V per-HART local interrupt controller driver Anup Patel
2020-05-30 12:01 ` Marc Zyngier
2020-05-31 5:36 ` Anup Patel
2020-05-31 9:33 ` Marc Zyngier
2020-05-31 10:06 ` Anup Patel
2020-05-31 10:53 ` Marc Zyngier
2020-06-01 4:09 ` Anup Patel [this message]
2020-06-01 7:41 ` Marc Zyngier
2020-06-01 9:13 ` Anup Patel
2020-06-01 9:33 ` Guo Ren
2020-05-30 10:07 ` [PATCH v6 4/6] clocksource/drivers/timer-riscv: Use per-CPU timer interrupt Anup Patel
2020-05-30 11:41 ` Marc Zyngier
2020-05-31 5:52 ` Anup Patel
2020-05-30 10:07 ` [PATCH v6 5/6] RISC-V: Remove do_IRQ() function Anup Patel
2020-05-30 10:07 ` [PATCH v6 6/6] RISC-V: Force select RISCV_INTC for CONFIG_RISCV Anup Patel
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