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

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Date:   Thu, 29 Jun 2017 17:22:28 +0200
From:   Andreas Färber <afaerber@...e.de>
To:     Arnd Bergmann <arnd@...db.de>,
        Thomas Liau <thomas.liau@...ions-semi.com>
Cc:     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

Am 29.06.2017 um 17:07 schrieb Arnd Bergmann:
>>> +static int s500_smp_boot_secondary(unsigned int cpu, struct task_struct *idle)
>>> +{
>>> +       unsigned long timeout;
>>> +       int ret;
>>> +
>>> +       ret = s500_wakeup_secondary(cpu);
>>> +       if (ret)
>>> +               return ret;
>>> +
>>> +       udelay(10);
>>> +
>>> +       spin_lock(&boot_lock);
>>> +
>>> +       /*
>>> +        * The secondary processor is waiting to be released from
>>> +        * the holding pen - release it, then wait for it to flag
>>> +        * that it has been released by resetting pen_release.
>>> +        */
>>> +       write_pen_release(cpu_logical_map(cpu));
>>> +       smp_send_reschedule(cpu);
>>> +
>>> +       timeout = jiffies + (1 * HZ);
>>> +       while (time_before(jiffies, timeout)) {
>>> +               if (pen_release == -1)
>>> +                       break;
>>> +       }
>>> +
>>> +       writel(0, timer_base_addr + OWL_CPU1_ADDR + (cpu - 1) * 4);
>>> +       writel(0, timer_base_addr + OWL_CPU1_FLAG + (cpu - 1) * 4);
>>> +
>>> +       spin_unlock(&boot_lock);
>>> +
>>> +       return pen_release != -1 ? -ENOSYS : 0;
>>> +}
>>
>> This looks more complicated than necessary. Why do you need the holding
>> pen when you have a register to start up the CPU?
>>
> 
> 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.

Regards,
Andreas

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