linux-kernel - Re: [RFC PATCH 5/5] arm64: qcom: add cpu operations

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Date:	Wed, 15 Apr 2015 15:53:51 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Al Stone <ahs3@...hat.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	Kumar Gala <galak@...eaurora.org>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"arm@...nel.org" <arm@...nel.org>,
	Abhimanyu Kapur <abhimany@...eaurora.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 5/5] arm64: qcom: add cpu operations

On Wed, Apr 15, 2015 at 10:04:25AM +0100, Mark Rutland wrote:
> On Tue, Apr 14, 2015 at 11:52:39PM +0100, Al Stone wrote:
> > On 04/14/2015 10:29 AM, Mark Rutland wrote:
> > >> diff --git a/Documentation/devicetree/bindings/arm/cpus.txt b/Documentation/devicetree/bindings/arm/cpus.txt
> > >> index 8b9e0a9..35cabe5 100644
> > >> --- a/Documentation/devicetree/bindings/arm/cpus.txt
> > >> +++ b/Documentation/devicetree/bindings/arm/cpus.txt
> > >> @@ -185,6 +185,8 @@ nodes to be present and contain the properties described below.
> > >>                           be one of:
> > >>                              "psci"
> > >>                              "spin-table"
> > > 
> > > In the case of these two, there's documentation on what the OS, FW, and
> > > HW are expected to do. There's a PSCI spec, and spin-table is documented
> > > in booting.txt (which is admittedly not fantastic).
> > > [snip...]
> > 
> > Perhaps a side topic, but I thought spin-table was being actively discouraged
> > for arm64.  Forgive me if I missed the memo, but is that not correct?
> 
> We prefer that people implement PSCI, and if they must use spin-table,
> each CPU has its own release address.
> 
> However, we don't want implementation-specific mechanisms, and
> spin-table is preferable to these.

An important aspect is that with spin-table you don't get CPU off or
suspend and some kernel functionality will be missing (kexec being one
of them).

-- 
Catalin
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