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Thread: Black notebook display, LVDS not detected anymore

  1. #1
    Join Date
    Dec 2013
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    Default Black notebook display, LVDS not detected anymore

    Hello,


    I own a HP 655 notebook (Hewlett-Packard HP 655 Notebook PC/1885, BIOS F.26 05/21/2013) with an integrated Radeon HD 7340.

    About two months ago, I updated the kernel and shut down the computer. For one subsequent boot with the new kernel, the computer worked fine.

    However, the next boot, the screen was constantly black, even on power-on, when the BIOS/EFI was still in full control.


    First I thought the computer was defective, but I noticed on HD activity that it apparently booted. Long story short, I connected an external display and it worked fine.


    After some simple diagnosis, I found that the LVDS isn't detected at all as if it wouldn't exist.

    dmesg gives me a single error message: "[drm:radeon_acpi_init] *ERROR* Cannot find a backlight controller"

    xrandr shows HDMI-0 and VGA-0 but not LVDS-0 as it was the case before the trouble started.


    I know what a display with a defective background controller looks like. This display, however, doesn't show anything at all.


    Here is the output of radeontool --debug

    radeontool --debug
    Found card 1002:9808 (30000)
    Radeon found. Base control address is 7fb730825000; base framebuffer address is 7fb720825000.
    reading RADEON_DAC_CNTL (58) is 00000000
    reading RADEON_LVDS_GEN_CNTL (2d0) is 00000000


    I didn't move the computer at all, so I guess a hardware fault would be rather unlikely.

    I suspect the kernel to have changed some registers, maybe something in EFI or some NVRAM parts
    that cause the computer to shut-down the LVDS immediately on boot.

    I even installed Windows on the computer using the external display, tried different Linux distributions
    and different kernel versions, flashed the BIOS to the most recent version, all to no avail.


    So I wonder if there is a possibility for this to be a software/EFI/NVRAM/... issue.

    Is there a way to check LVDS operation with radeontool?

    Is there any other way to get more detailed information about the issue, like reading special
    registers with radeontool?

  2. #2
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    Dec 2013
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    Default

    *bump*

    Here is someone who has similar issues, but updating the kernel didn't help.

    https://bbs.archlinux.org/viewtopic.php?id=159905

  3. #3
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    Dec 2013
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    What I already did:

    • Open the whole computer and display and replug all cables to make sure they're connected (LVDI cable and all others)
    • Install Windows 7 and 8 hoping the proprietary drivers could help
    • Update the BIOS to the most recent version
    • Remove the Battery for a day and reset the BIOS
    • Use efibootmgr to delete all EFI boot entries and manually add a new one
    • Try all kinds of boot parameters (radeon DPM on/off, backlight vendor and others, ACPI different vendors, ...)


    None of these helped.

    What I still need is a way to check if the hardware doesn't recognize the LVDS at all or if it's somehow disabled (does NVRAM offer such a possibility?)

  4. #4
    Join Date
    Oct 2012
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    Default

    What kernel are you using? Did you try an older kernel? Can you post logs?

    You said you installed windows and it didn't help.. To me looks like a hardware problem.

    Did you run sensors-detect while having radeon.hw_i2c=1 in the kernel command line ?
    I'm far from expert, but I remember reading something like this... And it looks like using sensors-detect and the radeon driver is a dangerous thing. From http://lm-sensors.org/#Latestnews:
    http://lists.lm-sensors.org/pipermai...il/035847.html
    http://lists.freedesktop.org/piperma...ry/052041.html

  5. #5
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    Quote Originally Posted by asdfblah View Post
    Did you run sensors-detect while having radeon.hw_i2c=1 in the kernel command line ?
    Yes, I had this kernel parameter enabled and ran sensors-detect at about that time.

    Is there any way to recover?

    My issue almost exactly matches http://lists.freedesktop.org/piperma...ry/052044.html but the LVDS output isn't recognized at all.


    Does anyone else own a HP 655 notebook? I'd like to compare the output values of i2c-tools.

  6. #6
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    Oct 2012
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    Quote Originally Posted by radeon View Post
    Yes, I had this kernel parameter enabled and ran sensors-detect at about that time.

    Is there any way to recover?

    My issue almost exactly matches http://lists.freedesktop.org/piperma...ry/052044.html but the LVDS output isn't recognized at all.


    Does anyone else own a HP 655 notebook? I'd like to compare the output values of i2c-tools.
    What model, exactly?

    I'd try to follow the instructions in that post, send that guy and email and ask people in IRC (freenode) if they have the same hardware to help. There are lots of channels related to linux and electronics, I guess someone will help you there. Try looking for the part numbers of your hardware. Also, see if HP can help you, etc. Try to get all the help you can get..

  7. #7
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    Dec 2013
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    Hello,


    the model is HP-655

    HP-655UE2180QX500NXN04La

    the HP Product Number is

    B6M65EA


    Does dmidecode show LVDS connectors?

    It doesn't show any on this notebook. Only CRT and HDMI.


    Handle 0x0014, DMI type 8, 9 bytes
    Port Connector Information
    Internal Reference Designator: J2A2
    Internal Connector Type: None
    External Reference Designator: CRT
    External Connector Type: DB-15 female
    Port Type: Video Port


    Handle 0x0015, DMI type 8, 9 bytes
    Port Connector Information
    Internal Reference Designator: J2A3
    Internal Connector Type: None
    External Reference Designator: HDMI
    External Connector Type: Other
    Port Type: Video Port

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