Re: [PATCH v2 6/6] [RFC] arm: use PSCI if available

From: Arnd Bergmann <arnd@arndb.de>
To: Will Deacon <will.deacon@arm.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	"xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"konrad.wilk@oracle.com" <konrad.wilk@oracle.com>,
	Ian Campbell <Ian.Campbell@citrix.com>,
	Marc Zyngier <Marc.Zyngier@arm.com>,
	"linux@arm.linux.org.uk" <linux@arm.linux.org.uk>,
	"nico@linaro.org" <nico@linaro.org>
Subject: Re: [PATCH v2 6/6] [RFC] arm: use PSCI if available
Date: Tue, 26 Mar 2013 15:46:49 +0000	[thread overview]
Message-ID: <201303261546.50194.arnd@arndb.de> (raw)
In-Reply-To: <20130326153730.GA22368@mudshark.cambridge.arm.com>

On Tuesday 26 March 2013, Will Deacon wrote:
> > They can even base the implementation of their smp_ops on the current
> > psci code, in order to facilitate that I could get rid of psci_ops
> > (which initialization is based on device tree) and export the psci_cpu_*
> > functions instead, so that they can be called directly by other smp_ops.
> 
> Again, I think this destroys the layering. The whole point is that the PSCI
> functions are called from within something that understands precisely how to
> talk to the firmware and what it is capable of.

Right, we probably the psci smp ops to be separate from the rest of the psci
code, but I also think that Stefano is right that we should let any platform
use the psci smp ops if possible, rather than having to implement their own.

> > > If this can indeed work for the virtual platforms (Xen and KVM), then I
> > > think it would be better expressed using `virt' smp_ops, which map directly
> > > to PSCI, rather than putting them here. Even then, it's tying KVM and Xen
> > > together on the firmware side of things...
> > 
> > Keep in mind that dom0 on Xen boots as a native machine (versatile
> > express or exynos5 for example) with a Xen hypervisor node on it.  We
> > would need to find a way to override the default machine smp_ops with
> > a set of xen_smp_ops early at boot.
> > I don't like this option very much, I think is fragile.
> 
> Why can't dom0 use whatever smp ops the native machine would use?

The part that I'm most interested in is making it possible for a platform
to kill off its native smp ops in the kernel by implementing the psci
ops. I think it's a good strategy to use psci by default if both 
platform and psci implementations are available.

	Arnd