[ltp] Re: [ibm-acpi-devel] thinkpad-acpi release 0.17-20071002 uploaded to ibm-acpi.sf.net

[Henrique de Moraes Holschuh]

On Wed, 03 Oct 2007, Chris Hanson wrote:
> Henrique de Moraes Holschuh wrote:
> > * Support for 16-level brightness for Lenovo thinkpads
> >   (X61, T61 *needs* this.  X60 likely does so, as well.  T60 appears not to,
> >    but I welcome tests, it should auto-detect).
> 
> This support works fine on my T60.  But I noticed a small problem: I tried

Thanks for testing, and for the report!

>   echo 15 > /sys/class/backlight/thinkpad_screen/brightness
> 
> which generated EINVAL, as expected.  But afterwards all values
> generated EINVAL, even reasonable ones such as 0 through 7.  EINVAL was
> also generated when trying to set the value through procfs, either by
> up/down or level N.  Prior to trying 15, the 0-7 values didn't signal
> EINVAL errors.

Can't reproduce this on 2.6.22 and a T43.  Given that the driver returns
EINVAL well before it even tries to poke the hardware, it should not make a
difference which thinkpad we try it on.  So, that leaves us with
thinkpad-acpi bugs, or a backlight class bug.  Which kernel version?

Also, just to be sure, cat
/sys/class/backlight/thinkpad_screen/max_brightness returns 7 in your T60,
correct?

> The kern.log is filled with messages like
> 
>   Oct  3 00:21:50 ravna kernel: set_level status: 0
> 
> which originate in "drivers/acpi/video.c".  My interpretation is that
> some variable in ACPI got set to a bad value and is now stuck there.

Should be impossible to happen as long as max_brightness is not 15 (not only
because of the backlight class, but also because it means thinkpad-acpi is
supposed to refuse to write such stuff to the hardware).  But a backlight
variable being stuck is not at all difficult to imagine.  Let's try to track
it down...

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh