linux-kernel - Re: Re : [HELP] Power management for embedded system

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Message-ID: <20060824101125.GA21439@flint.arm.linux.org.uk>
Date:	Thu, 24 Aug 2006 11:11:25 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	moreau francis <francis_moreau2000@...oo.fr>
Cc:	linux-pm@...ts.osdl.org, linux-kernel@...r.kernel.org
Subject: Re: Re : [HELP] Power management for embedded system

On Thu, Aug 24, 2006 at 09:37:39AM +0000, moreau francis wrote:
> Russell King wrote:
> > On Thu, Aug 24, 2006 at 08:44:25AM +0000, moreau francis wrote:
> >> Mips one seems to be a copy and paste of arm one and both of them
> >> have removed all APM bios stuff orginally part of i386 implementation.
> > 
> > The BIOS stuff makes no sense on ARM - there isn't a BIOS to do anything
> > with.
> 
> I haven't said that it has been widely/wrongly removed...

ROTFL!  No, you were stating that the APM bios stuff was removed, and
I gave the reason for it.  Why are you now objecting to my explaination?

> >> It doesn't seem that APM is something really stable and finished.
> > 
> > It's complete.  It's purpose is to provide the interface to userland so
> > that programs know about suspend/resume events, and can initiate suspends.
> > Eg, the X server.
> > 
> 
> Is there something specific to ARM in this implementation ? I don't think
> so and it's surely the reason why MIPS did copy it with almost no changes.

MIPS copied it because presumably it was useful for them.

> I understand that ARM implementation has been the first one but maybe now
> why not making it the common power management for embedded system that
> could be used by all arches which need it ?

It could well become a common interface.  But it is NOT power management
infrastructure.  It is merely a _userland_ interface.  Nothing more.  It
does not do anything other than that.

> BTW, why has apm_cpu_idle() logic been removed from ARM implementation ?

This APM is just a userland interface.  It has nothing to do with actual
power management.  CPU idling is handled entirely differently on ARM.

> > The power management really comes from the Linux drivers themselves,
> > which are written to peripherals off when they're not in use.  The other
> > power saving comes from things like cpufreq - again, nothing to do with
> > the magical "APM" or "ACPI" terms.
> 
> BTW why is it still called "APM" on ARM ?

That's what the userland interface is called on x86.  We could've called it
apm_userland_interface_emulation_and_not_a_power_management_infrastructure.c
but although that clearly states what it is, it would've been far too long
a name. 8)

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core
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