Re: [linux-sunxi] [RFC 0/7] ARM: sun9i: SMP support with Multi-Cluster Power Management

From: Nicolas Pitre <nicolas.pitre@linaro.org>
To: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Ian Campbell <ijc@hellion.org.uk>,
	wens@csie.org, Dave Martin <Dave.Martin@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-sunxi@googlegroups.com
Subject: Re: [linux-sunxi] [RFC 0/7] ARM: sun9i: SMP support with Multi-Cluster Power Management
Date: Mon, 18 May 2015 01:19:18 -0400 (EDT)	[thread overview]
Message-ID: <alpine.LFD.2.11.1505180112570.4843@knanqh.ubzr> (raw)
In-Reply-To: <20150517143816.GJ4004@lukather>

On Sun, 17 May 2015, Maxime Ripard wrote:

> Hi Ian,
> 
> On Sat, May 16, 2015 at 11:08:46AM +0100, Ian Campbell wrote:
> > On Thu, 2015-05-14 at 14:10 +0800, Chen-Yu Tsai wrote:
> > > This is my attempt to support SMP and CPU hot plugging on the Allwinner
> > > A80 SoC. The A80 is a big.Little processor with 2 clusters of 4x Cortex-A7
> > > and 4x Cortex-A15 cores.
> > 
> > I thought there was a preference these days to support this sort of
> > thing via support PSCI in the firmware, which allows for other things
> > such as non-secure-world etc.
> 
> Yes, it is the preferred way. Meaning that if someone wants to do that
> work, he's very much welcome and encouraged to do so. But if no one's
> doing it, then we still have to have a way to bringup the secondary
> CPUs.

And doing so in the kernel (at least initially) is simpler, and so much 
easier to fix when it is broken.  We've seen a few systems already where 
power management is crippled because no one is able/allowed/willing to 
fix the broken firmware.

Nicolas