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

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Message-ID: <ZQQDJT6MOaIOPmq5@shell.armlinux.org.uk>
Date:   Fri, 15 Sep 2023 08:09:25 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Salil Mehta <salil.mehta@...wei.com>
Cc:     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 02:29:13AM +0000, Salil Mehta wrote:
> On x86, during init, if the MADT entry for LAPIC is found to be
> online-capable and is enabled as well then possible and present

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 it's
completely fine if aarch64 does something else (maybe treating it
strictly as per the spec and ignoring online-capable.)

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