Detecting LCD Monitors.

Tue Aug 14 15:44:08 UTC 2007

On Mon, Aug 13, 2007 at 08:28:41PM -0400, D. Hugh Redelmeier wrote:
> Here's a rather confusing extract from my machine's Xorg.0.log:
> 
>      1	(II) NV(0): Probing for EDID on I2C bus B...
>      2	(II) NV(0): I2C device "DDC:ddc2" registered at address 0xA0.
>      3	(II) NV(0): I2C device "DDC:ddc2" removed.
> *    4	(--) NV(0): DDC detected a DFP:

Well DFP means digital flat panel.  Certainly good to know.

>      5	(II) NV(0): Manufacturer: DEL  Model: 4016  Serial#: 1194472500
>      6	(II) NV(0): Year: 2005  Week: 51
>      7	(II) NV(0): EDID Version: 1.3
>      8	(II) NV(0): Digital Display Input
> *    9	(II) NV(0): Max H-Image Size [cm]: horiz.: 64  vert.: 40
>     10	(II) NV(0): Gamma: 2.20
>     11	(II) NV(0): DPMS capabilities: Off; RGB/Color Display
> *   12	(II) NV(0): First detailed timing not preferred mode in violation of standard!
> *   13	(II) NV(0): redX: 0.640 redY: 0.343   greenX: 0.292 greenY: 0.611
>     14	(II) NV(0): blueX: 0.146 blueY: 0.074   whiteX: 0.313 whiteY: 0.331
>     15	(II) NV(0): Manufacturer's mask: 0
>     16	(II) NV(0): Supported additional Video Mode:
>     17	(II) NV(0): clock: 71.0 MHz   Image Size:  646 x 406 mm
>     18	(II) NV(0): h_active: 1280  h_sync: 1328  h_sync_end 1360 h_blank_end 1440 h_border: 0
>     19	(II) NV(0): v_active: 800  v_sync: 803  v_sync_end 809 v_blanking: 823 v_border: 0
>     20	(II) NV(0): Supported additional Video Mode:
>     21	(II) NV(0): clock: 268.0 MHz   Image Size:  646 x 406 mm
>     22	(II) NV(0): h_active: 2560  h_sync: 2608  h_sync_end 2640 h_blank_end 2720 h_border: 0
>     23	(II) NV(0): v_active: 1600  v_sync: 1603  v_sync_end 1609 v_blanking: 1646 v_border: 0
>     24	(II) NV(0): Monitor name: DELL 3007WFP
>     25	(II) NV(0): Serial No: JG5785CFG244
>     26	(II) NV(0): EDID (in hex):
>     27	(II) NV(0):     00ffffffffffff0010ac164034343247
>     28	(II) NV(0):     330f01038040287828fe87a3574a9c25
>     29	(II) NV(0):     13505400000001010101010101010101
>     30	(II) NV(0):     010101010101bc1b00a0502017303020
>     31	(II) NV(0):     360086962100001ab06800a0a0402e60
>     32	(II) NV(0):     3020360086962100001e000000fc0044
>     33	(II) NV(0):     454c4c20333030375746500a000000ff
>     34	(II) NV(0):     004a47353738354346473234340a0007
> *   35	(--) NV(0): CRTC 0 is currently programmed for DFP
> *   36	(II) NV(0): Using DFP on CRTC 0
>     37	(--) NV(0): Panel size is 2560 x 1600

That line looks awfully useful.  And of course the two modeline choices
below are in fact the only two valid settings on that screen, of which
the 2560x1600 is obviously the desired one.

>     38	(II) NV(0): Printing DDC gathered Modelines:
>     39	(II) NV(0): Modeline "1280x800"   71.00  1280 1328 1360 1440  800 803 809 823 -hsync +vsync
>     40	(II) NV(0): Modeline "2560x1600"  268.00  2560 2608 2640 2720  1600 1603 1609 1646 +hsync +vsync
> *   41	(II) NV(0): Panel is TMDS
>     42	(--) NV(0): VideoRAM: 262144 kBytes
>     43	(==) NV(0): Using gamma correction (1.0, 1.0, 1.0)
>     44	(II) NV(0): <default monitor>: Using hsync range of 49.31-98.71 kHz
>     45	(II) NV(0): <default monitor>: Using vrefresh range of 59.86-59.97 Hz
>     46	(II) NV(0): Estimated virtual size for aspect ratio 1.6000 is 2560x1600
>     47	(II) NV(0): Clock range:  12.00 to 400.00 MHz
>     48	(II) NV(0): Not using default mode "640x350" (hsync out of range)
> 
> Things to note:
> 
> Line 4 says that a Digital Flat Panel was detected.  Could that be
> what you are looking for?  Lines 35 and 36 also mention DFP.

Well certainly with the nvidia driver, this is useful info.  The fglrx
ati driver gives rather different output.

> Line 9 tells you the size of the display.  That could be used to tell
> the aspect ratio.  As well, if this were to get into the xorg.conf
> Monitor section's DisplaySize declaration, I think that X will scale
> fonts to make them readable for most people.
> 
> Line 41 says that the panel is TMDS.  Perhaps that strongly suggests LCD.
>   http://en.wikipedia.org/wiki/Transition_Minimized_Differential_Signaling
> 
> Line 12 says that the monitor violates some standard.
> 
> Line 12 seems to suggest that the data specifies a preferred mode.
> Perhaps that is what you shuld be using.

Interesting, although there is the issue that only the 1280x800 mode is
always going to work, while 2560x1600 only works with a dual link cable
and dual link port.  Perhaps that is why the data was arranged that way
so that the first mode was the mode that would always work, and the
prefered mode is the one that might not work if the system setup is
wrong.

> BTW, lines 12 and 13 were actually one originally: I broke them
> appart.  I would guess that this is an X bug.
> 
> Context:
> - Fedora 7 x86_64
> - nVidia 7800GTX
> - Dell 3007FPW  2560x1600 pixels
> - nv (open-source, 2d-only) driver
> - xorg-x11-server 1.3.0.0-9.fc7

--
Len SOrensen
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