From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jay Lan <jlan@sgi.com>
Date: Fri, 02 Feb 2007 15:21:41 +0000
Subject: Re: [Fastboot] [PATCH] kexec: Fix CONFIG_SMP=n compilation (ia64)
Message-Id: <45C35705.20505@sgi.com>
List-Id: <linux-ia64.vger.kernel.org>
References: <aec7e5c30702011838g6e9edd23sc782321aacb07297@mail.gmail.com>	<10EA09EFD8728347A513008B6B0DA77A086BD0@pdsmsx411.ccr.corp.intel.com> <20070202035714.GE16554@verge.net.au>
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To: Horms <horms@verge.net.au>
Cc: "Zou, Nanhai" <nanhai.zou@intel.com>, Magnus Damm <magnus@valinux.co.jp>, "Luck, Tony" <tony.luck@intel.com>, linux-ia64@vger.kernel.org, fastboot@lists.osdl.org, Andrew Morton <akpm@linux-foundation.org>, Magnus Damm <magnus.damm@gmail.com>, linux-kernel@vger.kernel.org

Horms wrote:
> On Fri, Feb 02, 2007 at 11:01:21AM +0800, Zou, Nanhai wrote:
>>>>>  void
>>>>>  machine_crash_shutdown(struct pt_regs *pt)
>>>>> @@ -132,11 +134,12 @@ kdump_cpu_freeze(struct unw_frame_info *
>>>>>       atomic_inc(&kdump_cpu_freezed);
>>>>>       kdump_status[cpuid] = 1;
>>>>>       mb();
>>>>> -     if (cpuid = 0) {
>>>>> -             for (;;)
>>>>> -                     cpu_relax();
>>>>> -     } else
>>>>> +#ifdef CONFIG_HOTPLUG_CPU
>>>>> +     if (cpuid != 0)
>>>>>               ia64_jump_to_sal(&sal_boot_rendez_state[cpuid]);
>>>>> +#endif
>>>>> +     for (;;)
>>>>> +             cpu_relax();
>>>>>  }
>>>> I trust ia64_jump_to_sal doesn't return.
>>> So do I. The main problem with the compilation seems to be that
>>> ia64_jump_to_sal() only exists if CONFIG_HOTPLUG_CPU=y.
>>> (include/asm-ia64/sal.h, arch/ia64/kernel/head.S)
>>>
>>  This may cause problem on SN platform. 
>> I remember SN requires cpu0 return to SAL rendez loop to do IRQ redirection.
>> However this needs SGI people to confirm...

SN needs slave cpus being returned to SAL rendez loop with the exception
of cpu0. It seems there is not a decent way to return cpu0, so we
decided to handle cpu0 in PROM. This above code change does not casue
problem on SN platform.

> 
> Does this mean that CONFIG_HOTPLUG_CPU may be required for kdump
> on the SN platform?

The SN platform uses the ia64_jump_to_sal() routine.

Thanks,
 - jay