linux-kernel - Re: [linux-sunxi] Re: [PATCH 2/3] ARM: sun8i: Add SMP support for the Allwinner A23

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Date:	Thu, 19 Mar 2015 10:18:43 +0100
From:	"maxime.ripard" <maxime.ripard@...e-electrons.com>
To:	"kevin.z.m.zh@...il.com" <kevin.z.m.zh@...il.com>
Cc:	"linux-sunxi@...glegroups.com" <linux-sunxi@...glegroups.com>,
	Chen-Yu Tsai <wens@...e.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Marc Zyngier <marc.zyngier@....com>
Subject: Re: [linux-sunxi] Re: [PATCH 2/3] ARM: sun8i: Add SMP support for
 the Allwinner A23

Hi Kevin,

On Thu, Mar 19, 2015 at 12:05:06PM +0800, kevin.z.m.zh@...il.com wrote:
> >> One question I couldn't find any answer to is that does the SMP bit is
> >> set in secondary_startup?
> >>
> >> I couldn't find where it was set, but it still looks like the right
> >> thing to do, so I would expect the code to do that.
> > 
> > I don't see it either. The sun8i code is just the sun6i code with the
> > power clamps removed. And sun6i secondary_startup was removed some time
> > ago in commit 1146b600044d ("ARM: sunxi: fix build for THUMB2_KERNEL").
> > 
> > ChenYu
>
> The SMP bit should be set in the function of "__v7_ca7mp_setup", which is located
> in the file:
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/mm/proc-v7.S?id=refs/tags/v4.0-rc4
> I'm not sure if this is your discussion.

It is, but I wasn't seeing it called anywhere in the secondary_startup
code path.

I was expecting a direct call, but it looks like it's a dynamic call,
with a function-pointer like call, that is indeed run both in the
kernel entry point and the secondary_startup.

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/kernel/head.S?id=refs/tags/v4.0-rc4#n389

Thanks!
Maxime

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

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