From: simon@sequanux•org (Simon Guinot)
To: linux-arm-kernel@lists•infradead.org
Subject: [lm-sensors] [PATCH v2] hwmon: add generic GPIO fan driver
Date: Thu, 21 Oct 2010 21:59:29 +0000 [thread overview]
Message-ID: <20101021215928.GS29120@kw.sim.vm.gnt> (raw)
In-Reply-To: <20101021144346.GA26460@ericsson.com>
Hi Guenter,
On Thu, Oct 21, 2010 at 07:43:46AM -0700, Guenter Roeck wrote:
> > >
> > > The combination of DIV_ROUND_UP() and DIV_ROUND_CLOSEST() causes inconsistency.
> > >
> > > Assume num_speed = 8, pwm is set to 128.
> > >
> > > set: 128 * (8 - 1) / 255 = 3.513 ==> 4
> > > get: 4 * 255 / (8 - 1) = 145.7 ==> 146
> > > set: 146 * (8 - 1) / 255 = 4.007 ==> 5
> > > get: 5 * 255 / (8 - 1) = 182.142 ==> 182
> > > set: 182 * (8 - 1) / 255 = 4.996 ==> 5
> > >
> > > Unless there is a really good reason to use DIV_ROUND_UP(), you might
> > > want to use DIV_ROUND_CLOSEST() instead.
> >
> > This choice is coherent with the rpm interface one and the reason is the
> > same: start the fan even with a low value. In your example, 36 is first
> > speed threshold.
> >
> Yes, but here it causes an inconsistency between setting and reporting.
> I don't expect the speed to change if I set the same value that was read.
> Exactly this happens if one writes 146 in my example. That is much worse
> than a potential startup problem, or the observation that pwm values below X
> don't start the fan.
Mmm. Convert a speed index into a low round pwm value (and not use
DIV_ROUND_CLOSEST() at all) fix the inconsistency too. If you agree,
I would prefer this option.
Thanks,
Simon
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next prev parent reply other threads:[~2010-10-21 21:59 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-20 16:37 [PATCH v2] hwmon: add generic GPIO fan driver Simon Guinot
2010-10-20 16:37 ` Simon Guinot
2010-10-20 16:59 ` Guenter Roeck
2010-10-20 19:10 ` Simon Guinot
2010-10-20 20:42 ` Guenter Roeck
2010-10-20 19:18 ` Russell King - ARM Linux
2010-10-20 20:06 ` Guenter Roeck
2010-10-21 6:41 ` Guenter Roeck
2010-10-21 14:06 ` Simon Guinot
2010-10-21 14:43 ` Guenter Roeck
2010-10-21 21:59 ` Simon Guinot [this message]
2010-10-21 22:16 ` [lm-sensors] " Guenter Roeck
2010-10-21 22:35 ` Simon Guinot
2010-10-21 22:44 ` [PATCH v3] " Simon Guinot
2010-10-22 1:51 ` Guenter Roeck
2010-10-22 12:25 ` Simon Guinot
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