linux-kernel - Re: [PATCH] panic: keep blinking in spite of long spin timer mode

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Message-Id: <201006032149.AA00423@tamuki.linet.gr.jp>
Date:	Fri, 04 Jun 2010 06:49:22 +0900
From:	TAMUKI Shoichi <tamuki@...et.gr.jp>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Anton Blanchard <anton@...ba.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andy Green <andy@...mcat.com>,
	TAMUKI Shoichi <tamuki@...et.gr.jp>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] panic: keep blinking in spite of long spin timer mode

Hello,

On Wed, 2 Jun 2010 11:34:46 -0700 Andrew Morton wrote:

> The whole panic-blink setup seems rather poorly thought out.
> 
> Would it not be better if a call to (*panic_blink)() were to simply set
> the state of the LED and then return?  So callers can do
> 
> 	int state = 0;
> 
> 	for ( ; ; ) {
> 		(*panic_blink)(state);
> 		state ^= 1;
> 		mdelay(MSEC_PER_SEC);
> 	}
> 
> ?

Your proposal is rather simpler than the current patch, indeed.

I carefully went into the proposal:

  - With this implementation, the time to call to mdelay() needs to be
    variable in order to change the speed of blinking.
  - It is not desirable that the period to call to touch_nmi_watchdog()
    or touch_softlockup_watchdog() depends on the speed of blinking.
  - We would like to leave the room that can be implemented as not only
    a simple blinking but also as a so-called morse blinking which con-
    tains useful information when kernel panics.

That being the reason, I will keep the current implementation that the
time to call mdelay() is a short constant (as 1ms usually).

BTW, there are some sanity checks or something in panic_blink_enter(),
which need not exist there, so I have moved them to appropriate place.

Thank you for the suggestion.  See you next PATCH v2.

Regards,
TAMUKI Shoichi
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