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Date:	Sun, 28 Dec 2014 00:28:20 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Gabriele Mazzotta <gabriele.mzt@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jean Delvare <jdelvare@...e.de>,
	Steven Honeyman <stevenhoneyman@...il.com>,
	Jochen Eisinger <jochen@...guin-breeder.org>,
	linux-kernel@...r.kernel.org, Valdis.Kletnieks@...edu
Subject: Re: [PATCH 3/3] i8k: Remove laptop specific config data (fan_mult,
 fan_max) from driver

On Sun, Dec 28, 2014 at 09:22:29AM +0100, Pali Rohár wrote:
> On Saturday 27 December 2014 15:13:28 Gabriele Mazzotta wrote:
> > On Thursday 25 December 2014 22:54:34 Gabriele Mazzotta wrote:
> > > On Thursday 18 December 2014 12:08:58 Pali Rohár wrote:
> > > > On Wednesday 10 December 2014 14:32:16 Gabriele Mazzotta 
> wrote:
> > > > > On Wednesday 10 December 2014 12:51:30 Pali Rohár wrote:
> > > > > > On Tuesday 09 December 2014 21:07:01 Pali Rohár wrote:
> > > > > > > Now we have autodetection code for fan multiplier
> > > > > > > and maximal fan speed so we do not need to have
> > > > > > > those constants for each laptop in kernel driver
> > > > > > > code.
> > > > > > > 
> > > > > > > Signed-off-by: Pali Rohár <pali.rohar@...il.com>
> > > > > > > ---
> > > > > > > !!!Please do not apply this patch until all affected
> > > > > > > machines will be tested!!!
> > > > > > > 
> > > > > > > I tested autodetection code only on Dell Latitude
> > > > > > > E6440 (where it worked). Other machines which needs
> > > > > > > to be tested:
> > > > > > > 
> > > > > > > Dell Latitude D520
> > > > > > > Dell Latitude E6540
> > > > > > > Dell Precision WorkStation 490
> > > > > > > Dell Studio
> > > > > > > Dell XPS M140 (MXC051)
> > > > > > > ---
> > > > > > 
> > > > > > Can somebody else with dell laptops test this patch
> > > > > > series?
> > > > > 
> > > > > i8k_get_fan_nominal_rpm() returns -22 on my XPS13, so
> > > > > nothing changed with this patch series applied.
> > > > > 
> > > > > Gabriele
> > > > 
> > > > So your BIOS cannot report nominal_rpm and because your
> > > > machine is not in dmi list, all 3 patches do nothing for
> > > > your machine.
> > > > 
> > > > But you need to set multiplier to 1, right?
> > > > 
> > > > What about this patch? (on top of 3/3)
> > > > 
> > > > --- a/drivers/char/i8k.c
> > > > +++ b/drivers/char/i8k.c
> > > > @@ -850,6 +850,10 @@ static int __init i8k_probe(void)
> > > > 
> > > >  		 */
> > > >  		
> > > >  		for (fan = 0; fan < I8K_FAN_COUNT; ++fan) {
> > > >  		
> > > >  			i8k_fan_mult[fan] = I8K_FAN_DEFAULT_MULT;
> > > > 
> > > > +			if (i8k_get_fan_rpm(fan) > I8K_FAN_MAX_RPM) {
> > > > +				i8k_fan_mult[fan] = 1;
> > > > +				continue;
> > > > +			}
> > > > 
> > > >  			for (val = 0; val < 256; ++val) {
> > > >  			
> > > >  				ret = i8k_get_fan_nominal_rpm(fan, val);
> > > >  				if (ret > I8K_FAN_MAX_RPM) {
> > > 
> > > Hi,
> > > 
> > > I'm sorry for replying only now, but I couldn't follow this
> > > thread closely and I'm a bit lost now. I haven't tested the
> > > suggested change, but I don't think it would work in a
> > > reliable way. It's not rare for the fan to be completely
> > > stopped, especially on boot. You are right though, 1 is the
> > > right multiplier.
> > 
> > I took a better look at the code and my laptop is indeed able
> > to report the nominal speed. The problem with the original
> > patch was that the first call of i8k_get_fan_nominal_rpm()
> > correctly returned -22 (the fan doesn't exist) and the loop
> > was terminated because of that. I tested the following patch
> > http://www.spinics.net/lists/kernel/msg1892101.html and the
> > fan multiplier auto detection worked.
> > 
> > I confirm that the suggested change in case the nominal speed
> > can't be retrieved is not OK as its outcome depends on the
> > current state of the fans.
> > 
> > > Guenter, while I was trying to catch up, I noticed that the
> > > support for the XPS 13 [1] will be added. May I ask you
> > > which revision of the laptop was tested? I own the 9333 one
> > > and I'm not sure that having i8k automatically loaded is a
> > > good idea. The reason is that reading and setting the speed
> > > of the right (and only) fan causes a freeze of the laptop
> > > of some milliseconds, enough to be annoying and noticeable.
> > > I'm worried of the effect this might have in the everyday
> > > use, users might start noticing random freezes because of
> > > one application that all the sudden is able to read the
> > > speed of the fan. I don't if the same happens on all the
> > > other Dell systems, this is the first and only Dell laptop
> > > I owned.
> > > 
> > > If the tested laptop wasn't the XPS13 9333 and this problem
> > > does not exists, would it be possible to make the
> > > DMI_PRODUCT_NAME string such that it matches only the
> > > tested revision? The string that identifies my laptop is
> > > "XPS13 9333".
> > > 

I am several thousand miles away from the XPS13 right now, so I can not check
it. As far as I recall, it was a 9333.

> > > Gabriele
> > > 
> > > [1] http://www.spinics.net/lists/kernel/msg1878801.html
> > 
> > I modified i8k so that it prints the time required to execute
> > the assembly code in i8k_smm(). Here what I got:
> > 
> > [ 4697.485130] i8k_smm asm: 1965800 ns    #pwm1
> > [ 4697.487383] i8k_smm asm: 1375057 ns    #temp3_input
> > [ 4697.489477] i8k_smm asm: 1112493 ns    #temp3_label
> > [ 4697.991687] i8k_smm asm: 500796086 ns  #fan1_input
> > [ 4697.998245] i8k_smm asm: 1957365 ns    #fan1_label
> > [ 4698.009190] i8k_smm asm: 1770247 ns    #temp1_input
> > [ 4698.014416] i8k_smm asm: 749734 ns     #temp1_label
> > [ 4698.019103] i8k_smm asm: 2503962 ns    #temp2_input
> > [ 4698.023490] i8k_smm asm: 1738982 ns    #temp2_label
> > 
> > As you can see, the time required to read the speed of the fan
> > is substantially higher than the combined time of all the
> > other reads.
> > 
> > Is the difference so big for the other systems that have been
> > tested?
> 
> It looks like we should not read fan rpm at startup for 
> multiplier autodetection... and only fan nominal speed.
> 
Yes, agreed. After all, we still have the module parameter to override it
if reading the nominal speed (and thus auto-detection) is not successful.

Guenter
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