[Bug 191137] Re: [Hardy] ACPI Embedded Controller (EC) stops boot when kernel boot 'quiet' option is enabled

[TJ]

Vladimir, that is great news!

I'm building test kernels for several ACPI related bugs at present so I
can't test it immediately, but if that proves to deal with this issue as
a workaround until we can locate the root-cause, that is better in many
ways than removing "quiet".

I wanted to record here my preliminary investigation into what "quiet"
does that is different from a regular boot without it.

Firstly, the existing levels:

$ cat /proc/sys/kernel/printk
4       4       1       7

That's console_loglevel, default_message_level, minimum_console_level,
default_console_loglevel. You'll notice above that the default level
(the last value) is 7 which is used when "quiet" *is not* passed to the
kernel.

In init/main.c::quiet_kernel()

 console_loglevel = 4;

In include/linux/kernel.h:

#define console_loglevel (console_printk[0])

and in kernel/printk.c:

#define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
#define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */

int console_printk[4] = {
	DEFAULT_CONSOLE_LOGLEVEL,	/* console_loglevel */
	DEFAULT_MESSAGE_LOGLEVEL,	/* default_message_loglevel */
	MINIMUM_CONSOLE_LOGLEVEL,	/* minimum_console_loglevel */
	DEFAULT_CONSOLE_LOGLEVEL,	/* default_console_loglevel */
};

So when running at level 4 less messages get printed to console and
therefore 'things' will happen faster than at the default level 7 when
more messages are being generated. That suggests a timing issue as I
said previously *unless* somehow some code is caught in a conditional
expression based on loglevel.

-- 
[Hardy] ACPI Embedded Controller (EC) stops boot when kernel boot 'quiet' option is enabled
https://bugs.launchpad.net/bugs/191137
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