linux-kernel - Re: [PATCH v4 20/28] ARM: owl: Implement CPU enable-method for S500

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Message-ID: <CAK8P3a1vCKkZ8i=MLQXHX5ZowWQGbqiMo3gQz1E9RV+8sSGfpA@mail.gmail.com>
Date:   Thu, 29 Jun 2017 17:50:15 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Andreas Färber <afaerber@...e.de>
Cc:     Thomas Liau <thomas.liau@...ions-semi.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        mp-cs@...ions-semi.com,
        张东风 <zhangdf@...ions-semi.com>,
        刘炜 <liuwei@...ions-semi.com>,
        张天益 <tyzhang@...ions-semi.com>,
        96boards@...obotics.com, support@...aker.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH v4 20/28] ARM: owl: Implement CPU enable-method for S500

On Thu, Jun 29, 2017 at 5:22 PM, Andreas Färber <afaerber@...e.de> wrote:
> Am 29.06.2017 um 17:07 schrieb Arnd Bergmann:
>>
>> It seems you missed my question here. Can you please follow up, and
>> if possible send a patch to remove the pen_release logic that appears
>> to be unnecessary here?
>
> I do not have any documentation on these registers, only the downstream
> code that I forward-ported here. If you tell me what you mean exactly, I
> can do some testing and if it still works submit a patch to simplify it.
>
> Comments from the so far quiet Actions Semi side would help, too.

IIRC, there are two ways to implement SMP bootup: either you have
registers to tell the secondary CPU how to start up out of reset or they
get put into a holding pen during early boot where they spin waiting
for a variable to get written.

However, doing both is not necessary. See for example mach-sunxi
for an example without the holding pen. I think you can just delete
half of your file to do the same.

        Arnd