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Old 04-15-10, 10:32 PM   #1
peepingtom
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Default NVIDIA Quadro NVS 3100M on Lenovo Thinkpad T510: NVIDIA Backlight Control Causes Buzz

The backlight brightness controls on this laptop with NVS 3100m work while running Nouveau or when using a text mode VT, but not while running X and using proprietary NVIDIA drivers. It is possible to force the nvidia driver to control the backlight, but this causes the LED backlight to buzz. This occurs constantly whenever the backlight is set to less than 100%. The noise changes in tone/pitch as the backlight levels are altered, and the noise continues until the backlight is set to maximum intensity. This noise does not occur when using the open source nouveau driver, which has its own method of controlling the backlight, and it does not occur when the brightness is changed in a text mode VT while running the nvidia driver.

The behaviour as been confirmed via thinkwiki.org . Because this is an LED backlight which does not have an inverter, it is unexpected that this noise should occur. This leads me to believe that the nvidia driver is sending the wrong level of power (voltage?) to the LED array, and is possibly stressing the physical components.

Is there any information I could provide that would help a developer solve this problem?

The hardware brightness buttons on this laptop always affect /sys/devices/virtual/backlight/acpi_video0/brightness, which accepts values up to 15. If the brightness value is raised while running X, /sys/devices/virtual/backlight/acpi_video0/brightness is changed but the actual backlight is not affected. If I then switch to a text mode VT and press the backlight up button, /sys/devices/virtual/backlight/acpi_video0/brightness is increased again and the backlight is set to the appropriate level. This level will persist when I switch back to X.

I have written a bug report for Ubuntu Lucid Lynx at Launchpad.net
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Old 04-26-10, 12:24 PM   #2
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Default Re: NVIDIA Quadro NVS 3100M on Lenovo Thinkpad T510: NVIDIA Backlight Control Causes

So I know that it's not possible to use Nouveau's backlight controls with the proprietary NVIDIA driver, but the nouveau driver also adds a new backlight interface to sysFS (ie. this interface doesn't exist when using the NVIDIA driver). Since the framebuffer driver that runs text-mode VTs is always running, and it runs concurrently with the NVIDIA driver, is it possible to use the VT's method in X? If it too adds a special section to sysFS, i'd like to find it.

Does anyone know a good method for monitoring changes in sysFS? I know it's a virtual filesystem so many standard methods don't work. Ive tried using tree and then searching for interesting stuff, but I hope there's a better method.

Is it safe to assume that the NVIDIA driver has a table of values for the backlights of different laptops? I hope so, then these Thinkpad T510s don't need a special backlight driver. I think it's a very bad idea have the NVIDIA driver control this backlight by default, at least in the driver's current state. I'm still worried that this buzzing noise indicates long-term physical damage. At the very least, it's annoying.
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Old 04-27-10, 03:31 PM   #3
danix
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Default Re: NVIDIA Quadro NVS 3100M on Lenovo Thinkpad T510: NVIDIA Backlight Control Causes

I've been trying to get a ThinkPad T510 so that we can take a look at this issue, but haven't been able to get my hands on one so far. In the meantime, could somebody provide a dump of the ACPI DSDT table for one of these machines? Run the following as root:

acpidump -b -t DSDT -o DSDT.out #this dumps the DSDT table to "DSDT.out" in your current directory
iasl -d DSDT.out #this disassembles the dump file and produces "DSDT.dsl"

Thanks
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Old 05-03-10, 07:53 PM   #4
peepingtom
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Default Re: NVIDIA Quadro NVS 3100M on Lenovo Thinkpad T510: NVIDIA Backlight Control Causes

Thanks again for looking into this for us!

This is a disassembled DSDT from my t510 with latest BIOS updates.
Attached Files
File Type: bz2 DSDT.dsl.tar.bz2 (32.5 KB, 184 views)
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Old 07-17-10, 12:22 PM   #5
peepingtom
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Default Re: NVIDIA Quadro NVS 3100M on Lenovo Thinkpad T510: NVIDIA Backlight Control Causes

There is still discussion about t410 and t510 backlights in a thread about Quadro FX 880Ms here: http://www.nvnews.net/vbulletin/showthread.php?t=145105 but all recent stuff is unrelated to this buzzing issue.


This issue persists with NVIDIA's 256.35 driver. Have any NVIDIA employees had access to a T510 to check this issue yet? Thank you for not yet enabling backlight control by default, the brightness values passed are still most likely incorrect!
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Old 12-03-10, 05:17 PM   #6
peepingtom
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Default Re: NVIDIA Quadro NVS 3100M on Lenovo Thinkpad T510: NVIDIA Backlight Control Causes

NVIDIA developers, has anyone yet had access to a Lenovo ThinkPad T510 to test this backlight issue? The bug reports on launchpad.net have been active for months, and this issue is confirmed. https://bugs.launchpad.net/ubuntu/+s...rs/+bug/562005
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Old 03-21-11, 06:10 PM   #7
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Default Re: NVIDIA Quadro NVS 3100M on Lenovo Thinkpad T510: NVIDIA Backlight Control Causes

This issue persists with the 270.30 driver.
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Old 04-22-11, 09:29 PM   #8
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Default Re: NVIDIA Quadro NVS 3100M on Lenovo Thinkpad T510: NVIDIA Backlight Control Causes

I filed a bug report with nvidia over a month ago and have received no comment or resolution.
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Old 06-10-11, 02:50 AM   #9
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Default Re: NVIDIA Quadro NVS 3100M on Lenovo Thinkpad T510: NVIDIA Backlight Control Causes

Polite bump, issue persists.
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