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

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Date:	Mon, 18 May 2015 11:04:17 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:	Ian Campbell <ijc@...lion.org.uk>, wens@...e.org,
	Dave Martin <Dave.Martin@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-sunxi@...glegroups.com
Subject: Re: [linux-sunxi] [RFC 0/7] ARM: sun9i: SMP support with
 Multi-Cluster Power Management

Hi Nicolas,

On Mon, May 18, 2015 at 01:19:18AM -0400, Nicolas Pitre wrote:
> 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.

To be fair, our platform support is done by hobbyist, and our only
implementation of PSCI is done through mainline u-boot, which means we
have an easy way to fix any issue we might have, and that it's
possible, otherwise we wouldn't have it at all.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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