linux-kernel - Re: [PATCH] arm64: skip cpu nodes marked as disabled in DT

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Date:   Thu, 26 Apr 2018 19:54:06 +0000
From:   Rohit Khanna <rokhanna@...dia.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Catalin Marinas <catalin.marinas@....com>
CC:     "will.deacon@....com" <will.deacon@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thierry Reding <treding@...dia.com>,
        Alexander Van Brunt <avanbrunt@...dia.com>,
        Bo Yan <byan@...dia.com>,
        Jason Sequeira <jsequeira@...dia.com>,
        Mark Rutland <mark.rutland@....com>,
        Vignesh Radhakrishnan <vigneshr@...dia.com>,
        "Krishna Sitaraman" <ksitaraman@...dia.com>
Subject: Re: [PATCH] arm64: skip cpu nodes marked as disabled in DT

Thanks Lorenzo for pulling out the old thread.

So just to make sure my understanding is correct from the discussion on that thread, below is not a preferred approach.

"If CPUs are marked as disabled in the devicetree, make sure they do
not exist in the system CPU information and CPU topology information."


The reason is because - "The meaning of disabled for cpus in ePAPR is that the cpu is offline
(i.e. in a spinloop or wfi), not that the cpu is unavailable."


Preferred approach is -
"Since with this approach the DT should change anyway if on different
>    hardware devices based on the same chip you want to allow booting a
>    different number of CPUs, why do not we remove the cpu nodes instead of
>    disabling them"

Thanks
Rohit
________________________________________
From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Sent: Thursday, April 26, 2018 3:18 AM
To: Catalin Marinas; Rohit Khanna
Cc: will.deacon@....com; linux-kernel@...r.kernel.org; Thierry Reding; Alexander Van Brunt; Bo Yan; Jason Sequeira; Mark Rutland
Subject: Re: [PATCH] arm64: skip cpu nodes marked as disabled in DT

On Thu, Apr 26, 2018 at 08:25:14AM +0100, Catalin Marinas wrote:
> On Wed, Apr 25, 2018 at 11:36:06PM +0000, Rohit Khanna wrote:
> > Adding few other folks.
>
> It looks fine to me but cc'ing Mark and Lorenzo (and it should have been
> posted on linux-arm-kernel@...ts.infradead.org).
>
> > From: Rohit Khanna
> > Sent: Wednesday, April 25, 2018 4:08 PM
> > To: catalin.marinas@....com; will.deacon@....com
> > Cc: linux-kernel@...r.kernel.org; Rohit Khanna
> > Subject: [PATCH] arm64: skip cpu nodes marked as disabled in DT
> >
> > Skip the CPU nodes that are marked as disabled in DT.
> >
> > Bug 1828570

That's not information that can be used in its current form, which
bug-tracking system ?

> > Signed-off-by: Rohit Khanna <rokhanna@...dia.com>
> > Reviewed-on: http://git-master/r/1245333

If it is a public mailing list discussion the

Link:

tag and the lkml redirector should be used, I do not know what the
redirector used here is though.

Process is defined here:

https://www.kernel.org/doc/html/latest/process/submitting-patches.html

> > Reviewed-by: Alexander Van Brunt <avanbrunt@...dia.com>
> > ---
> >  arch/arm64/kernel/smp.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> > index f3e2e3aec0b0..2b4371b0948d 100644
> > --- a/arch/arm64/kernel/smp.c
> > +++ b/arch/arm64/kernel/smp.c
> > @@ -578,6 +578,10 @@ static void __init of_parse_and_init_cpus(void)
> >         for_each_node_by_type(dn, "cpu") {
> >                 u64 hwid = of_get_cpu_mpidr(dn);
> >
> > +               /* Check to see if the cpu is disabled */
> > +               if (!of_device_is_available(dn))
> > +                       goto next;
> > +

This was discussed a long time ago and kind of dropped - I digged the
thread out of archives for everyone's information:

http://lists.infradead.org/pipermail/linux-arm-kernel/2013-June/174324.html

Lorenzo