linux-kernel - Re: [PATCH v4 3/6] thermal: Added Bang-bang thermal governor

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Date:	Tue, 22 Jul 2014 16:59:02 +0200
From:	Peter Feuerer <peter@...e.net>
To:	Zhang Rui <rui.zhang@...el.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andreas Mohr <andi@...as.de>, Borislav Petkov <bp@...e.de>,
	Javi Merino <javi.merino@....com>
Subject: Re: [PATCH v4 3/6] thermal: Added Bang-bang thermal governor

Hi,

Zhang Rui writes:

> On Mon, 2014-07-21 at 11:29 +0200, Borislav Petkov wrote:
>> On Sun, Jul 20, 2014 at 02:51:17AM +0200, Peter Feuerer wrote:
>> > The bang-bang thermal governor uses a hysteresis to switch abruptly on
>> > or off a cooling device.  It is intended to control fans, which can
>> > not be throttled but just switched on or off.
>> > Bang-bang cannot be set as default governor as it is intended for
>> > special devices only.  For those special devices the driver needs to
>> > explicitely request it.
>> > 
>> > Cc: Andrew Morton <akpm@...ux-foundation.org>
>> > Cc: Zhang Rui <rui.zhang@...el.com>
>> > Cc: Andreas Mohr <andi@...as.de>
>> > Cc: Borislav Petkov <bp@...e.de>
>> > Cc: Javi Merino <javi.merino@....com>
>> > Signed-off-by: Peter Feuerer <peter@...e.net>
>> > ---
>> >  drivers/thermal/Kconfig         |  10 +++
>> >  drivers/thermal/Makefile        |   1 +
>> >  drivers/thermal/gov_bang_bang.c | 131 ++++++++++++++++++++++++++++++++++++++++
>> >  drivers/thermal/thermal_core.c  |   5 ++
>> >  drivers/thermal/thermal_core.h  |   8 +++
>> >  5 files changed, 155 insertions(+)
>> >  create mode 100644 drivers/thermal/gov_bang_bang.c
>> > 
>> > diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
>> > index f9a1386..cdddf09 100644
>> > --- a/drivers/thermal/Kconfig
>> > +++ b/drivers/thermal/Kconfig
>> > @@ -84,6 +84,16 @@ config THERMAL_GOV_STEP_WISE
>> >  	  Enable this to manage platform thermals using a simple linear
>> >  	  governor.
>> >  
>> > +config THERMAL_GOV_BANG_BANG
>> > +	bool "Bang Bang thermal governor"
>> > +	default y
>> 
>> Right, this is problematic.
>> 
>> When people are faced with the new selection after doing oldconfig, they
>> can say yes or no.
>> 
>> However, as acerhdf depends on it now, prompting the user to
>> unconditionally says yes is kinda redundant. Especially as this governor
>> is not supposed to be default anyway.
>> 
>> Actually you don't need the Kconfig prompt at all as this is a sort-of
>> "internal" governor and devices select it. IOW, it should be "default n"
>> and ACERHDF will do "select THERMAL_GOV_BANG_BANG". Something like that
>> at least.
>> 
> I agree with this approach.

Yes, you are right, this looks better.  Then the "depend on 
THERMAL_GOV_BANG_BANG" could be removed from acerhdf Kbuild, as the "select" 
will take care acerhdf is compiled with THERMAL_GOV_BANG_BANG enabled, 
right?

-- 
--peter;
--
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