linux-kernel - Re: [PATCH] i8k: increase fan limit to 3

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Message-ID: <20140522155458.GI12759@t520.home>
Date:	Thu, 22 May 2014 12:54:58 -0300
From:	Flavio Leitner <fbl@...hat.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Flavio Leitner <fbl@...close.org>
Subject: Re: [PATCH] i8k: increase fan limit to 3

On Thu, May 22, 2014 at 08:10:48AM -0700, Guenter Roeck wrote:
> On Wed, May 21, 2014 at 11:19:28PM -0300, Flavio Leitner wrote:
> > From: Flavio Leitner <fbl@...close.org>
> > 
> > It is possible to increase left fan speed on a
> > DELL Precision 490n system up to 3.
> > 
> >     value    fan rpm
> >       1      35460
> >       2      64740
> >       3      78510
> > 
> > Signed-off-by: Flavio Leitner <fbl@...close.org>
> > ---
> >  drivers/char/i8k.c       | 4 ++--
> >  include/uapi/linux/i8k.h | 3 ++-
> >  2 files changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c
> > index d915707..99180f0 100644
> > --- a/drivers/char/i8k.c
> > +++ b/drivers/char/i8k.c
> > @@ -519,7 +519,7 @@ static ssize_t i8k_hwmon_show_pwm(struct device *dev,
> >  	status = i8k_get_fan_status(index);
> >  	if (status < 0)
> >  		return -EIO;
> > -	return sprintf(buf, "%d\n", clamp_val(status * 128, 0, 255));
> > +	return sprintf(buf, "%d\n", clamp_val(status * 128, 0, 384));
> 
> pwm value range is limited to (0, 255), so we'll have to find another
> solution.

You mean in the hw? Because the code today just multiply by 128 so
you have 0, 128 and 256 as possible pwm values. See below.

> I think we'll have to define a per-system data structure
> which holds the fan speed range and the fan multiplier, and attach it
> to the dmi data. Currently, .driver_data is used directly to override
> the fan multiplier; it will have to point to a configuration data
> structure with both fan multiplier and maximum fan speed value.
> Unless someone has a better idea, of course.

Sounds good to me.  It could provide a generic one that works as
today in case there is no specific per-system data structure.

It could also include the status multiplier so that for systems with
levels off, minimum and maximum then use x128 and systems with more
states can use another multiplier.

I volunteer to test on precision 490n and on latitude D520.

fbl
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