linux-kernel - Re: [RFC PATCH 3/5] RISC-V: Add cpu

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Message-ID: <20180822060353.GA27106@infradead.org>
Date:   Tue, 21 Aug 2018 23:03:53 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Anup Patel <anup@...infault.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Damien Le Moal <Damien.LeMoal@....com>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Atish Patra <atish.patra@....com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 3/5] RISC-V: Add cpu_operatios structure

On Tue, Aug 21, 2018 at 10:34:38PM +0530, Anup Patel wrote:
> The cpu_operations is certainly required because SOC vendors will add
> vendor-specific mechanism to selectively bringing-up CPUs/HARTs instead
> of all CPUs entering Linux kernel simultaneously. In fact, we might also end-up
> having CPU ON/OFF operations in SBI.

Your forgot an essential part in your analysis:  Right now we only have
one single way to deal with cpu on/offlining, and that is the dummy WFI
kind.  Once other ways show up we can build proper infrastructure, but
until then this is just a white elephant as we have no idea how these
abstractions will look like.

And my hope is that we'll just see new SBI calls, in which case we'll
just need SBI and dummy version and can avoid all the indirect calls.