linux-kernel - Re: [PATCH 1/1] ARM: STi: Restore secondary CPU's bringup

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Message-ID: <20181218172748.GQ26090@n2100.armlinux.org.uk>
Date:   Tue, 18 Dec 2018 17:27:48 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Patrice CHOTARD <patrice.chotard@...com>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] ARM: STi: Restore secondary CPU's bringup

On Tue, Dec 18, 2018 at 05:05:18PM +0000, Patrice CHOTARD wrote:
> Hi Russell
> 
> On 12/18/18 4:52 PM, Russell King - ARM Linux wrote:
> > On Tue, Dec 18, 2018 at 03:48:13PM +0100, patrice.chotard@...com wrote:
> >> From: Patrice Chotard <patrice.chotard@...com>
> >>
> >> Due to pen_release and boot_lock removal, secondary CPU's bringup
> >> was broken. Restore CPU's bringup by reworking properly
> >> .smp_prepare_cpus and .smp_boot_secondary STi callbacks.
> > 
> > Sorry, maybe I don't understand your commit message, but you seem to be
> > saying that removal of the pen_release and boot_lock broke STi's secondary
> > CPU bring up?  Please clarify, and explain how that happened.
> 
> Correct, CPU1 failed to come online.
> 
> It seems that writing secondary_startup address at cpu-release-addr in
> .smp_prepare_cpus callback was too early.
> 
> Doing it in .smp_boot_secondary callback, insures that secondary_data
> struct is populated in __cpu_up() (stack, pgdir and swapper_pg_dir fields).

Ah, you're saying that it causes the CPU to jump to secondary_startup
while the boot CPU is in smp_prepare_cpus()?  What triggers the CPU
to jump to the address written to cpu_strt_ptr?  What you're saying
seems to suggest that it's the write to that address, rather than the
IPI that's sent in sti_boot_secondary().

If the IPI in sti_boot_secondary() isn't doing anything, it ought to
be removed.  It'd also be a good idea to document what's going on as
comments in the code for future maintanence.

> If you are ok, i will pick up your patch [1] and this one to prepare a
> STi pull-request.

Yes, although I'll have to delay patch 9 as a result.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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