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 <20190115155600.GC13095@infradead.org>
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From:   Anup Patel <anup@brainfault.org>
Date:   Sat, 19 Jan 2019 10:55:58 +0530
Message-ID: <CAAhSdy2Oe44Mw66rphPHGU69DN1bnyhXH3xjrQ6DvLNsVVqgSw@mail.gmail.com>
Subject: Re: [PATCH v4 4/5] irqchip: sifive-plic: Differentiate between PLIC
 handler and context
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Palmer Dabbelt <palmer@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Cooper <jason@lakedaemon.net>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Atish Patra <atish.patra@wdc.com>,
        linux-riscv@lists.infradead.org,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>
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On Tue, Jan 15, 2019 at 9:26 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Thu, Dec 27, 2018 at 04:48:20PM +0530, Anup Patel wrote:
> > We explicitly differentiate between PLIC handler and context because
> > PLIC context is for given mode of HART whereas PLIC handler is per-CPU
> > software construct meant for handling interrupts from a particular
> > PLIC context.
> >
> > To achieve this differentiation, we rename "nr_handlers" to "nr_contexts"
> > and "nr_mapped" to "nr_handlers" in plic_init().
>
> Not sure what this differenciates that we previously didn't.  As far
> as I can tell it just is a slight naming cleanup.

There is a disconnect between PLIC documentation and PLIC driver.

If we have 8 HARTs then we can have 16 PLIC contexts whereas PLIC
handlers (SW construct) are always same as number of HARTs. In other
words, there will be separate PLIC context for M-mode and S-mode of a
HART.

Linux runs in S-mode so we can only use PLIC context meant for S-mode.
This means per-CPU handlers in PLIC driver only handle PLIC S-mode
context of a HART.

This patch makes PLIC driver more readable and matching PLIC HW
documentation by differentiating between PLIC handler and PLIC
context.

Regards,
Anup