Nouveau - Apr 2014 - [Bug 78106] New: Reported fan rpm is twice the actual value (NVC0)

https://bugs.freedesktop.org/show_bug.cgi?id=78106

          Priority: medium
            Bug ID: 78106
          Assignee: nouveau at lists.freedesktop.org
           Summary: Reported fan rpm is twice the actual value (NVC0)
        QA Contact: xorg-team at lists.x.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: mdop at seznam.cz
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: unspecified
         Component: Driver/nouveau
           Product: xorg

Created attachment 98224
  --> https://bugs.freedesktop.org/attachment.cgi?id=98224&action=edit
Kernel log

I have Gigabyte GTX 560 Ti Ultra Durable (01:00.0 VGA compatible controller:
NVIDIA Corporation GF114 [GeForce GTX 560 Ti] (rev a1)) and Nouveau doesn't
report correct fan speed. Reported value is exactly twice the actual speed. 

$ pacman -Q | grep nouveau
nouveau-dri 10.1.1-2
xf86-video-nouveau 1.0.10-2
$ sensors
...
nouveau-pci-0100
Adapter: PCI adapter
fan1:        6840 RPM
temp1:        +31.0?C  (high = +95.0?C, hyst =  +3.0?C)
                       (crit = +105.0?C, hyst =  +5.0?C)
                       (emerg = +135.0?C, hyst =  +5.0?C)
...

When I follow Documentation/thermal/nouveau_thermal and the speed to 100%,
nouveau reports "fan1: 6840 RPM" while the highest reported RPM by
Windows
(both Gigabyte tools and CPU-Z) is 3390 or 3420 RPM. Similar to when I set the
lowest speed (I have modified bios and my pwm1_min is 30) nouveau reports
"fan1: 3180 RPM" while Windows shows 1560 or 1590 RPM.
Could that be because the card has two physical fans? Reporting the speed of
single fan would make more sense IMHO.

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--- Comment #1 from Marcel Dopita <mdop at seznam.cz> ---
Created attachment 98225
  --> https://bugs.freedesktop.org/attachment.cgi?id=98225&action=edit
Xorg log

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--- Comment #2 from Martin Peres <martin.peres at ensi-bourges.fr> ---
Hi Marcel,

I was expecting to get a bug report on that much sooner. I will need to dive in
the vbios tables again to fix this.

The way fan speed is calculated is by reading the number of impulsions sent by
the hw tachometer. The tachometer has 1/2/4 or 8 pulses per turn. I couldn't
find information in the vbios as for how many pulses per turn I should expect.
I made it to work for all my cards (the same value worked everywhere) and
thought maybe NVIDIA forced manufacturers to use fans with the right number of
pulses per rotation (although it was weird).

Could you extract your vbios[0] and attach it to this bug report? It will help
me in my quest to find the byte I'm looking for!

Thanks!

[0] http://nouveau.freedesktop.org/wiki/DumpingVideoBios/

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--- Comment #3 from Marcel Dopita <mdop at seznam.cz> ---
Created attachment 98232
  --> https://bugs.freedesktop.org/attachment.cgi?id=98232&action=edit
Bioses

I'm attaching original bios for my card (1), bios which I modified and
flashed
under Windows (2) and the dumped one (3).
All three seem to differ so I'm attaching them all. I hope that modifying of
bios (lower min fan threshold from 40 to 30) is not causing this issue. Let me
know if you need me to verify it with stock bios. You have all the bioses but I
can verify it if it's too much trouble looking in the bios rom. I just hate
noise ;)

Thanks for looking into it.

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Martin Peres <martin.peres at ensi-bourges.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Martin Peres <martin.peres at ensi-bourges.fr> ---
Hi Marcel,

I had a look at your problem last week and the patch landed in Ben Skeggs'
tree:
http://cgit.freedesktop.org/~darktama/nouveau/commit/?id=0a6c57d0bbbffca7346627974c15b1d348c1fcb5

The fix will land in Linux 3.15. It could be backported, but I'm not sure it
is
worth the effort.

Thanks for the reporting this issue!

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