From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCH 2/2] ARM: tegra: moving the clock gating procedure to tegra_cpu_kill Date: Fri, 21 Dec 2012 14:23:17 -0700 Message-ID: <50D4D345.6030804@wwwdotorg.org> References: <1355970519-28200-1-git-send-email-josephl@nvidia.com> <1355970519-28200-2-git-send-email-josephl@nvidia.com> <50D34467.9000006@wwwdotorg.org> <1356083897.26029.187.camel@jlo-ubuntu-64.nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1356083897.26029.187.camel-yx3yKKdKkHfc7b1ADBJPm0n48jw8i0AO@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Joseph Lo , Will Deacon Cc: Peter De Schrijver , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: linux-tegra@vger.kernel.org On 12/21/2012 02:58 AM, Joseph Lo wrote: > On Fri, 2012-12-21 at 01:01 +0800, Stephen Warren wrote: >> On 12/19/2012 07:28 PM, Joseph Lo wrote: >>> The tegra_cpu_die was be executed by the CPU itslf. So the clock gating >>> procedure won't be executed after the CPU hardware shutdown code. Moving >>> the clock gating procedure to tegra_cpu_kill that will be run by another >>> CPU after the CPU died. >> >> Hmmm. I wonder if this is enough to make kexec-on-Tegra-with-SMP-enabled >> work without explicitly hot-unplugging all the CPUs first... An >> implementation of cpu_kill() was a major part of what was missing. I >> thought an implementation of cpu_kill() would require a bunch of code >> from cpu_die() too. Does this patch assume cpu_die() has executed first, >> and only then cpu_kill() will work, or can cpu_kill() be used on its own? >> > Yes, the tegra_cpu_die must be run first then tegra_cpu_kill. Because > the tegra_cpu_die shutdown the CPU by itself, then we can clock gate the > CPU in tegra_cpu_kill. If the tegra_cpu_kill be run itself, the system > will be hung in wait_for_reset(CPU). > > About the kexec issue, it's complicate. Your solution should be the > right solution. And we should implement the hardware shutdown code in > cpu_die not cpu_kill. I suspect this issue can be reproduced on all ARM > platform. Because the smp_send_stop can't really shutdown the secondary > CPU core if just call machine_shutdown without disable_nonboot_cpu. And > in platform_shutdown and platform_reboot case, the secondary CPU already > been offlined and killed before this function be called. Does any other > ARM SMP platform can run kexec without any issue? > > (I will check if we can do some HW shutdown in tegra_cpu_kill. For ex, > just clock gate the CPU without wait_for_reset.) Will, Joseph's thoughts above pretty much match mine re: kexec. In the kexec thread I started earlier, I talked about replacing: void machine_shutdown(void) { #ifdef CONFIG_SMP smp_send_stop(); #endif } with something like: void machine_shutdown(void) { #ifdef CONFIG_HOTPLUG_CPU disable_nonboot_cpus(); #elifdef CONFIG_SMP smp_send_stop(); #endif } and you'd responded "I think you're better off using what we currently have and hanging your code off platform_cpu_kill.". What exactly did you mean by "what we currently have"; did you mean that cpu_kill() should work without cpu_die() having executed on the target CPU itself first, so Tegra should simply implement cpu_kill()? As Joseph says above, I'm not sure that will work. Any more detailed thoughts you have here would be greatly appreciated. Thanks.