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Re: [PATCH] MIPS: OCTEON: Improve _machine_halt implementation.

To: David Daney <ddaney.cavm@gmail.com>
Subject: Re: [PATCH] MIPS: OCTEON: Improve _machine_halt implementation.
From: Wladislav Wiebe <wladislav.kw@gmail.com>
Date: Wed, 29 May 2013 08:09:01 +0200
Cc: linux-mips@linux-mips.org, ralf@linux-mips.org, David Daney <david.daney@cavium.com>, Maxim Uvarov <muvarov@gmail.com>
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Hi,

On 24/05/13 19:23, David Daney wrote:
> From: David Daney <david.daney@cavium.com>
> 
> As noted by Wladislav Wiebe:
>    $ halt
>    ..
>    Sent SIGKILL to all processes
>    Requesting system halt
>    [66.729373] System halted.
>    [66.733244]
>    [66.734761] =====================================
>    [66.739473] [ BUG: lock held at task exit time! ]
>    [66.744188] 3.8.7-0-sampleversion-fct #49 Tainted: G           O
>    [66.750202] -------------------------------------
>    [66.754913] init/21479 is exiting with locks still held!
>    [66.760234] 1 lock held by init/21479:
>    [66.763990]  #0:  (reboot_mutex){+.+...}, at: [<ffffffff801776c8>] 
> SyS_reboot+0xe0/0x218
>    [66.772165]
>    [66.772165] stack backtrace:
>    [66.776532] Call Trace:
>    [66.778992] [<ffffffff805780a8>] dump_stack+0x8/0x34
>    [66.783972] [<ffffffff801618b0>] do_exit+0x610/0xa70
>    [66.788948] [<ffffffff801777a8>] SyS_reboot+0x1c0/0x218
>    [66.794186] [<ffffffff8013d6a4>] handle_sys64+0x44/0x64
> 
> This is an alternative fix to the one sent by Wladislav.  We kill the
> watchdog for each CPU and then spin in WAIT with interrupts disabled.
> This is the lowest power mode for the OCTEON.  If we were to spin with
> interrupts enabled, we would get a continual stream of warning messages
> and backtraces from the lockup detector, so I chose to disable
> interrupts.
> 

good alternative!

Thanks.
--
Wladislav Wiebe


> Signed-off-by: David Daney <david.daney@cavium.com>
> Cc: Maxim Uvarov <muvarov@gmail.com>
> Cc: Wladislav Wiebe <wladislav.kw@gmail.com>
> ---
>  arch/mips/cavium-octeon/setup.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/mips/cavium-octeon/setup.c b/arch/mips/cavium-octeon/setup.c
> index b0baa29..01b1b3f 100644
> --- a/arch/mips/cavium-octeon/setup.c
> +++ b/arch/mips/cavium-octeon/setup.c
> @@ -428,13 +428,16 @@ static void octeon_restart(char *command)
>   */
>  static void octeon_kill_core(void *arg)
>  {
> -     mb();
> -     if (octeon_is_simulation()) {
> -             /* The simulator needs the watchdog to stop for dead cores */
> -             cvmx_write_csr(CVMX_CIU_WDOGX(cvmx_get_core_num()), 0);
> +     if (octeon_is_simulation())
>               /* A break instruction causes the simulator stop a core */
> -             asm volatile ("sync\nbreak");
> -     }
> +             asm volatile ("break" ::: "memory");
> +
> +     local_irq_disable();
> +     /* Disable watchdog on this core. */
> +     cvmx_write_csr(CVMX_CIU_WDOGX(cvmx_get_core_num()), 0);
> +     /* Spin in a low power mode. */
> +     while (true)
> +             asm volatile ("wait" ::: "memory");
>  }
>  
>  
> 


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