linux-kernel - Re: [RFC PATCH v2 27/35] ACPICA: Add new MADT GICC flags fields [code first?]

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Date:   Fri, 15 Sep 2023 14:43:05 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Salil Mehta <salil.mehta@...wei.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        James Morse <james.morse@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>,
        "x86@...nel.org" <x86@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "jianyong.wu@....com" <jianyong.wu@....com>,
        "justin.he@....com" <justin.he@....com>
Subject: Re: [RFC PATCH v2 27/35] ACPICA: Add new MADT GICC flags fields
 [code first?]

On Fri, Sep 15, 2023 at 09:34:46AM +0000, Salil Mehta wrote:
> > > Note that the ACPI spec says enabled + online-capable isn't defined.
> > >
> > > "The information conveyed by this bit depends on the value of the
> > > Enabled bit. If the Enabled bit is set, this bit is reserved and
> > > must be zero."
> > >
> > > So, if x86 is doing something with the enabled && online-capable
> > > state (other than ignoring the online-capable) then technically it
> > > is doing something that the spec doesn't define
> > 
> > And so it is wrong.
> 
> Or maybe, specification has not been updated yet. code-first?

What is the point in speculating. If you want to speculate about it,
fine, but please don't use speculation as a reason that "oh we need
to sort this out before we can merge the patches".

This is precisely why engineers are bad at producing products. They
like to continually tweak the design, and the design never gets out
the door. You need someone who is a project manager to tell engineers
when to stop. Without a project manager to do that, eventually the
project fades into insignificance because it becomes no longer relevant
or has its funding cut.

Hotplug VCPU on aarch64 feels exactly like that - it seems to be an
engineer project that is just going to for-ever rumble on and never
actually see the light of day.

So please - stop speculating and lets get vCPU hotplug *actually*
delivered and usable. Even if it's not 100% perfect.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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