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Old 01-10-10, 04:07 PM   #1
hasfill
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Default 195.30: same EDID interpreted differently on VGA and DVI connectors! Must be a bug?

Using NVIDIA-Linux-x86_64-195.30 and a Dell SP2309W monitor (native resolution 2048x1152),
the same EDID data is read (up to 4 bytes):-

hexdump of edid.bin when using VGA cable:
--------------------------------------------------------

0000000 ff00 ffff ffff 00ff ac10 d01b 5253 3044
0000010 132c 0301 330e 781d 18ea a955 3753 25ad
0000020 5013 a554 004b 4f71 8081 00b3 0101 0101
0000030 0101 0101 0101 3d3b a000 8080 4021 2030
0000040 0035 22fe 0011 1a00 0000 ff00 5400 3439
0000050 4630 4139 3054 5244 0a53 0000 fd00 3800
0000060 1e55 145c 0a00 2020 2020 2020 0000 fc00
0000070 4400 4c45 204c 5053 3332 3930 0a57 4b00
0000080


hexdump of edid.bin when using DVI cable:-
-----------------------------------------------------


0000000 ff00 ffff ffff 00ff ac10 d01c 5253 3044
0000010 132c 0301 3380 781d 18ea a955 3753 25ad
0000020 5013 a554 004b 4f71 8081 00b3 0101 0101
0000030 0101 0101 0101 3d3b a000 8080 4021 2030
0000040 0035 22fe 0011 1a00 0000 ff00 5400 3439
0000050 4630 4139 3054 5244 0a53 0000 fd00 3800
0000060 1e55 115c 0a00 2020 2020 2020 0000 fc00
0000070 4400 4c45 204c 5053 3332 3930 0a57 db00
0000080


$ diff edid.bin_vga_hexdump edid.bin_DVI_hexdump
1,2c1,2
< 0000000 ff00 ffff ffff 00ff ac10 d01b 5253 3044
< 0000010 132c 0301 330e 781d 18ea a955 3753 25ad
---
> 0000000 ff00 ffff ffff 00ff ac10 d01c 5253 3044
> 0000010 132c 0301 3380 781d 18ea a955 3753 25ad
7,8c7,8
< 0000060 1e55 145c 0a00 2020 2020 2020 0000 fc00
< 0000070 4400 4c45 204c 5053 3332 3930 0a57 4b00
---
> 0000060 1e55 115c 0a00 2020 2020 2020 0000 fc00
> 0000070 4400 4c45 204c 5053 3332 3930 0a57 db00

------------------------------------------------------------------
$ cmp -l edid.bin_vga edid.bin_DVI
11 33 34
21 16 200
100 24 21
128 113 333

--------------------------------------------------------------------------
After much experimentation, I found that

Option "ModeValidation" "noMaxPClkCheck"

allowed the monitor to use its native 2048x1152:
"2048x1152"x0.0 156.75 2048 2096 2128 2208 1152 1155 1160 1185 +hsync -vsync (71.0 kHz)


The problem seems to be that the DVI EDID reports a maximum pixel clock
of 155MHz:

(--) Jan 09 20:40:08 NVIDIA(0): DELL SP2309W (DFP-0): 155.0 MHz maximum pixel clock
(--) Jan 09 20:40:08 NVIDIA(0): DELL SP2309W (DFP-0): Internal Single Link TMDS


but 2048x1152 requires 156.75MHz.

I found a suggestion that this was a monitor firmware bug in a report on a similar
problem with a Samsung Syncmaster:
Manufacturer: SAM Model: 21e Serial#: xxxxxxxxxx

That report was more than two years ago, so it seems that there are various monitor models
with the same problem.

Can someone confirm that this really is a bug rather than a valid variation/extension of the EDID
specification? If a bug, cannot nvidia get the monitor manufacturers to fix their firmware? Or should we blacklist Samsung and Dell monitors for use with "other" operating systems?

I can try to get a firmware upgrade from Dell myself, but need to confirm that the DVI EDID
block above (or is it a separate TMDS encoder bit rate) is actually wrong.

There is more information towards the end of http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=498632

Help please!

ael
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Old 01-10-10, 04:53 PM   #2
zbiggy
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Default Re: 195.30: same EDID interpreted differently on VGA and DVI connectors! Must be a bu

Code:
(--) Jan 10 12:16:27 NVIDIA(0): NEC LCD1560NX (DFP-0): 165.0 MHz maximum pixel clock
165MHz is max pixel clock for single DVI according to specs and my monitor Edid.

If monitor has VGA and DVI output it had different EDID for those connectors. This is normal because VGA and DVI-D are different interfaces. For example my NEC 1560NX panel has DVI and VGA output. The EDID information is different for these connectors because VGA is analog and my DVI-D cable is digital only. I think edid code is common for VGA and DVI in nvidia driver because these is no difference in edid specs between connector types.
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Old 01-10-10, 07:20 PM   #3
zander
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Default Re: 195.30: same EDID interpreted differently on VGA and DVI connectors! Must be a bu

It is common for monitors to advertise different capabilities depending on the interface used (analog vs. digital, etc.). GPUs also have different hardware limitations depending on the display connector type: the maximum pixel clock of a single-link TMDS encoder is much lower than that of a legacy DAC, for example. To drive high-resolution devices via DVI, you generally need a dual-link connection.
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Old 01-11-10, 11:19 AM   #4
hasfill
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Default Re: 195.30: same EDID interpreted differently on VGA and DVI connectors! Must be a bu

Thanks for the replies. I should have included more info in my original post,
but was trying to be brief.
I have read http://en.wikipedia.org/wiki/Extende...ification_data, so I expected
byte 20 to differ. That said, that specification did not seem to match the results of a ddcprobe
(via the VGA interface):

vbe: VESA 3.0 detected.
oem: NVIDIA
vendor: NVIDIA Corporation
product: nv40 Board - p212-1 Chip Rev
memory: 131072kb
mode: 640x400x256
mode: 640x480x256
mode: 800x600x16
mode: 800x600x256
mode: 1024x768x16
mode: 1024x768x256
mode: 1280x1024x16
mode: 1280x1024x256
mode: 320x200x64k
mode: 320x200x16m
mode: 640x480x64k
mode: 640x480x16m
mode: 800x600x64k
mode: 800x600x16m
mode: 1024x768x64k
mode: 1024x768x16m
mode: 1280x1024x64k
mode: 1280x1024x16m
edid:
edid: 1 3
id: d01b
eisa: DELd01b
serial: 30445253
manufacture: 44 2009
input: separate sync, composite sync, sync on green, analog signal.
screensize: 51 29
gamma: 2.200000
dpms: RGB, active off, suspend, standby
timing: 720x400@70 Hz (VGA 640x400, IBM)
timing: 640x480@60 Hz (VGA)
timing: 640x480@75 Hz (VESA)
timing: 800x600@60 Hz (VESA)
timing: 800x600@72 Hz (VESA)
timing: 800x600@75 Hz (VESA)
timing: 1024x768@87 Hz Interlaced (8514A)
timing: 1024x768@75 Hz (VESA)
ctiming: 1152x864@75
ctiming: 1280x1024@60
ctiming: 1680x1680@60
dtiming: 2048x1152@59
monitorserial: T940F9AT0DRS
monitorrange: 30-92, 56-85
monitorname: DELL SP2309W

----------------------------------------------------------------------------------------
The same ddcprobe via the DVI-D interface fails:-

vbe: VESA 3.0 detected.
oem: NVIDIA
vendor: NVIDIA Corporation
product: nv40 Board - p212-1 Chip Rev
memory: 131072kb
mode: 640x400x256
mode: 640x480x256
mode: 800x600x16
mode: 800x600x256
mode: 1024x768x16
mode: 1024x768x256
mode: 1280x1024x16
mode: 1280x1024x256
mode: 320x200x64k
mode: 320x200x16m
mode: 640x480x64k
mode: 640x480x16m
mode: 800x600x64k
mode: 800x600x16m
mode: 1024x768x64k
mode: 1024x768x16m
mode: 1280x1024x64k
mode: 1280x1024x16m
edid:
edidfail

---------------------------------------------------

Ok, but I didn't properly explain the problem. It is simple. When the SP2309W monitor is connected
on the VGA interface, all is well. The correct 2048x1152 native resolution is selected.

However, when connected on the DVI-D it cannot be selected unless I use
Option "ModeValidation" "noMaxPClkCheck"
to force the pixel clock check off.

As for the maximum pixel clock on the DVI-D,
http://en.wikipedia.org/wiki/DVI-D says

"The DVI specification mandates a fixed single link maximum pixel clock frequency of 165 MHz, where all display modes that require less than this must use single link mode, and all those that require more must switch to dual link mode."

But Xorg.0.log from the nvidia driver on the DVI-D interface (noMaxPClkCheck on) says:-

(--) Jan 09 20:40:08 NVIDIA(0): Connected display device(s) on GeForce 6800 at PCI:1:0:0:
(--) Jan 09 20:40:08 NVIDIA(0): DELL SP2309W (DFP-0)
(--) Jan 09 20:40:08 NVIDIA(0): DELL SP2309W (DFP-0): 155.0 MHz maximum pixel clock
(--) Jan 09 20:40:08 NVIDIA(0): DELL SP2309W (DFP-0): Internal Single Link TMDS
(II) Jan 09 20:40:08 NVIDIA(0): Assigned Display Device: DFP-0

The DVI cable supplied with the monitor is single link. I suppose I could buy a dual link cable and try that. Could there be a typo somewhere in the driver where "155MHZ" is used instead of
"165MHz"?

However I see

5471: DESCRIPTOR BLOCK 1
5455: Pixel Clock (in 10 kHz) or 0 (55 MSB 54 LSB)

which is 3d3b! This is exactly 156.75MHz! Thus the dvi-edid pixel rate given by the monitor
is correct. So this is certainly a bug in the driver?

Summary: the dvi-edid from the monitor is 156.75MHz, but the driver gets 155MHz?
Conclusion: a bug in 195.30? {Or the monitor edid format confuses the driver somehow?}
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Old 01-11-10, 11:32 AM   #5
zander
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Default Re: 195.30: same EDID interpreted differently on VGA and DVI connectors! Must be a bu

(...)
(--) Jan 09 20:40:08 NVIDIA(0): Connected display device(s) on GeForce 6800 at PCI:1:0:0:
(--) Jan 09 20:40:08 NVIDIA(0): DELL SP2309W (DFP-0)
(--) Jan 09 20:40:08 NVIDIA(0): DELL SP2309W (DFP-0): 155.0 MHz maximum pixel clock
(--) Jan 09 20:40:08 NVIDIA(0): DELL SP2309W (DFP-0): Internal Single Link TMDS
(II) Jan 09 20:40:08 NVIDIA(0): Assigned Display Device: DFP-0
(...)
The maximum pixel clock reported by the driver in this case is that of the GPU, i.e. its internal TMDS encoder does not support pixel clocks above 155MHz.
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Old 01-11-10, 12:16 PM   #6
hasfill
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Default Re: 195.30: same EDID interpreted differently on VGA and DVI connectors! Must be a bu

Ah. It is the GPU! Could the log message not make that a bit clearer??
As it mentions the monitor rather than the GPU it is very misleading.... I see the logic
in retrospect, but still.

Thanks so much for the clarification...

ael
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