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

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Date:   Wed, 19 Dec 2018 11:28:32 +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 Wed, Dec 19, 2018 at 10:31:35AM +0000, Patrice CHOTARD wrote:
> Hi Russell
> 
> On 12/18/18 6:27 PM, Russell King - ARM Linux wrote:
> > 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
> 
> Yes
> 
> > 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().
> 
> At platform startup, an U-Bootrom firmware initialize secondary CPU and
> make it spinning waiting for a jump address to be written at cpu_strt_ptr.
> 
> I didn't pay attention to the IPI, you are right IPI is useless, i will
> remove it.

Okay, in that case may I suggest an alternative to taking my patch
which will break this, and then fixing it in a subsequent patch -
please merge the two patches together so it becomes one "clean up"
patch which doesn't cause any breakage.

Thanks.

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