Bug 26840

Summary: [GM965][intel] Black screen on external VGA
Product: xorg Reporter: Stefano Avallone <stavallo>
Component: Driver/intelAssignee: ykzhao <yakui.zhao>
Status: RESOLVED NOTOURBUG QA Contact: Xorg Project Team <xorg-team>
Severity: normal    
Priority: medium CC: michael.fu, yakui.zhao
Version: 7.5 (2009.10)   
Hardware: x86-64 (AMD64)   
OS: Linux (All)   
Whiteboard:
i915 platform: i915 features:
Attachments:
Description Flags
Xorg.0.log
none
dmesg.log
none
intel_reg_dumper log none

Description Stefano Avallone 2010-03-02 08:23:47 UTC
Created attachment 33685 [details]
Xorg.0.log

I get a black screen (no signal) on external VGA when trying:

xrandr --output VGA1 --mode 1024x768

I have a laptop with 965GM, kernel 2.6.33, xorg 1.7.5, libdrm 2.4.18, mesa 
7.7, xf86-video.intel 2.10.0 as packaged by Archlinux 64-bit. I am running KDE 
4.4.

I also tried to restart X server after connecting the VGA cable, but I still 
get no output on VGA, while getting a proper resolution (matching those on the 
VGA monitor) on LVDS1.

I am attaching:

- Xorg.0.log (with ModeDebug enabled)
- dmesg.log (with drm.debug=0x06)
- intel_reg_dumper.log

resulting from plugging the VGA cable during boot (before X started).

Thanks!
Comment 1 Stefano Avallone 2010-03-02 08:24:52 UTC
Created attachment 33686 [details]
dmesg.log
Comment 2 Stefano Avallone 2010-03-02 08:26:27 UTC
Created attachment 33687 [details]
intel_reg_dumper log
Comment 3 ykzhao 2010-03-03 00:15:33 UTC
Will you please do the following commands and see whether the VGA monitor can work?
   >xrandr --output VGA1 --mode 1024x768 --refresh 60
   >xrandr --output VGA1 --mode 1280x1024 --refresh 60

Do you have an opportunity to try another monitor and see whether the monitor can work well?

thanks.
Comment 4 Stefano Avallone 2010-03-03 00:30:10 UTC
>  xrandr --output VGA1 --mode 1024x768 --refresh 60
>  xrandr --output VGA1 --mode 1280x1024 --refresh 60
 
Both commands work, thanks. I will try later with another monitor.
I consider it at least a regression, because things used to work with this monitor without specifying the refresh rate. If you want me to test a patch, please let me know.

Thanks.
Comment 5 Michael Fu 2010-03-03 21:21:59 UTC
(In reply to comment #4)
> >  xrandr --output VGA1 --mode 1024x768 --refresh 60
> >  xrandr --output VGA1 --mode 1280x1024 --refresh 60
> 
> Both commands work, thanks. I will try later with another monitor.
> I consider it at least a regression, because things used to work with this
> monitor without specifying the refresh rate. If you want me to test a patch,
> please let me know.
> 
> Thanks.
> 

any hint when does it becomes broken for you? did you do a system upgrade?

in dmesg it says VGA-1 is disconnected while in xorg.log it says VGA is connected...
Comment 6 Stefano Avallone 2010-03-04 01:16:19 UTC
> any hint when does it becomes broken for you? did you do a system upgrade?

Well, it worked with Debian 32-bit and kernel 2.6.31. Recently, I installed Archlinux 64-bit (shipping kernel 2.6.32.8) and noticed this issue. 
 
> in dmesg it says VGA-1 is disconnected while in xorg.log it says VGA is
> connected...

Maybe this is due to the fact that I plugged the VGA cable during the boot, just before the X server started. So, maybe at the time I plugged the VGA cable, the drm module had been already loaded. 

I also tried with a projector having a single refresh rate (60 Hz) at 1024x768 and I had no problem by using xrandr --output VGA1 --mode 1024x768


Comment 7 Michael Fu 2010-03-04 05:53:32 UTC
(In reply to comment #6)
> 
> I also tried with a projector having a single refresh rate (60 Hz) at 1024x768
> and I had no problem by using xrandr --output VGA1 --mode 1024x768
> 

so VGA works ok with the projector, right? at least we narrowed down the bug a bit...
Comment 8 Stefano Avallone 2010-03-04 06:56:17 UTC
> 
> so VGA works ok with the projector, right? at least we narrowed down the bug a
> bit...
> 

Yes. xrandr --output VGA1 --mode 1024x768 was enough to send the output to the projector.
xrandr --output VGA1 --mode 1024x768 was *not* enough to send the output to a VGA monitor (normally used with a desktop PC). In this case I have to add --refresh 60 to make it work.

thanks.
Comment 9 ykzhao 2010-03-04 18:10:19 UTC
> Yes. xrandr --output VGA1 --mode 1024x768 was enough to send the output to the
> projector.
> xrandr --output VGA1 --mode 1024x768 was *not* enough to send the output to a
> VGA monitor (normally used with a desktop PC). In this case I have to add
> --refresh 60 to make it work.

Hi, 
    Thanks for the test.
    When the VGA monitor is used, it seems that it will report some display modes whose refresh rate is 85. If the display mode with refresh rate 85 is configured, the external VGA monitor can't work. If the display mode with refresh rate 60 is configured, it can work normally.

    When the projector is used, maybe it won't report the display mode whose refresh rate is 85. In such case it can work normally.

    Can the issue be related with the monitor?   

> 
> thanks.
> 


Comment 10 ykzhao 2010-03-22 02:00:49 UTC
From the comment #9 it seems that this issue is related with monitor. When the higher refresh rate is used, the monitor can't work well. If we can get the info about the range of hsync/vsync from the EDID, we can add this info to check whether the display mode falls into the correct range. 
   But unfortunately we can't get any useful info about the range of hsync/vsync from the EDID.

So this bug will be rejected as it is not the bug of our driver.

Thanks.
  

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