linux-kernel - Re: 2.6.31-rc2: thinkpad boots with backlight low

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Message-ID: <20090716000621.GA23073@khazad-dum.debian.net>
Date:	Wed, 15 Jul 2009 21:06:21 -0300
From:	Henrique de Moraes Holschuh <hmh@....eng.br>
To:	Tobias Diedrich <ranma+kernel@...edrich.de>,
	Pavel Machek <pavel@....cz>,
	kernel list <linux-kernel@...r.kernel.org>,
	ibm-acpi@....eng.br, ibm-acpi-devel@...ts.sourceforge.net
Subject: Re: 2.6.31-rc2: thinkpad boots with backlight low

On Thu, 16 Jul 2009, Tobias Diedrich wrote:
> Ok, after compiling it as a module and trying a few variations, it
> seems that on my X41 Tablet only brightness_mode=2 works, that is
> TPACPI_BRGHT_MODE_UCMS_STEP.

Ok...

> This is contrasted by thinkpad_acpi.c which states:
> |if (acpi_evalf(ec_handle, NULL, "HBRV", "qd"))
> |	/* T40-T43, R50-R52, R50e, R51e, X31-X41 */
> |	brightness_mode = TPACPI_BRGHT_MODE_ECNVRAM;
> |else
> |	/* all other IBM ThinkPads */
> |	brightness_mode = TPACPI_BRGHT_MODE_UCMS_STEP;
> 
> So TPACPI_BRGHT_MODE_ECNVRAM looks broken somehow?

Does the brightness change if you mess with /proc/acpi/ibm/brightness ? If
it doesn't, then it means your thinkpad doesn't use the EC to control
brightness.

And that will, of course, cause the driver to set the brightness in NVRAM to
zero (but it *should* do so for shutdown as well, not just machine-restart.
You may have uncovered two bugs, not just one), which will be honoured by
the BIOS on the next reboot/power up.

> I assume that the autodetection finds the HBRV acpi function and
> selects the former, resulting in a not working backlight control.

Yes.

Please send me by private mail the output of acpidump and dmidecode (so that
I will have them both in the same place).  I will blacklist your thinkpad to
force TPACPI_BRGHT_MODE_UCMS_STEP.

I wonder if other Intel GMA900 thinkpads also need this blacklisting,
though... this is the first report I got about HBRV not being good enough.

-- 
  "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
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