It appears 2560x1440 was a fake mode created by the open source driver. It's not a mode that is officially supported by the monitor itself, whose data I have decoded below:
EDID version: 1.4
Manufacturer: GSM Model 23305 Serial Number 181370
Made in week 5 of 2016
Digital display
10 bits per primary color channel
DisplayPort interface
Maximum image size: 60 cm x 34 cm
Gamma: 2.20
DPMS levels: Standby
Supported color formats: RGB 4:4:4, YCrCb 4:4:4, YCrCb 4:2:2
Default (sRGB) color space is primary color space
First detailed timing includes the native pixel format and preferred refresh rate
Color Characteristics
Red: 0.6523, 0.3349
Green: 0.3046, 0.6367
Blue: 0.1484, 0.0615
White: 0.3134, 0.3291
Established Timings I & II
640x480 59.940 Hz 4:3 31.469 kHz 25.175 MHz (DMT)
800x600 60.317 Hz 4:3 37.879 kHz 40.000 MHz (DMT)
1024x768 60.004 Hz 4:3 48.363 kHz 65.000 MHz (DMT)
Standard Timings
1152x864 59.959 Hz 4:3 53.783 kHz 81.750 MHz (EDID 1.4 source: CVT)
1152x864 60.000 Hz 4:3 53.700 kHz 81.624 MHz (EDID 1.3 source: GTF)
1280x1024 60.020 Hz 5:4 63.981 kHz 108.000 MHz (DMT)
1280x720 60.000 Hz 16:9 45.000 kHz 74.250 MHz (DMT)
1600x900 60.000 Hz 16:9 60.000 kHz 108.000 MHz (DMT, RB)
1920x1080 60.000 Hz 16:9 67.500 kHz 148.500 MHz (DMT)
1280x800 59.810 Hz 16:10 49.702 kHz 83.500 MHz (DMT)
Detailed mode: Clock 533.280 MHz, 600 mm x 340 mm
3840 3848 3992 4000 ( 8 144 8)
2160 2214 2219 2222 ( 54 5 3) +hsync -vsync VertFreq: 60.000 Hz, HorFreq: 133.320 kHz
Detailed mode: Clock 266.640 MHz, 600 mm x 340 mm
3840 3848 3992 4000 ( 8 144 8)
2160 2214 2219 2222 ( 54 5 3) +hsync -vsync VertFreq: 30.000 Hz, HorFreq: 66.660 kHz
Display Range Limits
Monitor ranges (GTF): 56-61 Hz V, 30-135 kHz H, max dotclock 560 MHz
Display Product Name: LG Ultra HD
Has 1 extension block
Checksum: 0x11
It appears 2560x1440 was a fake mode created by the open source driver. It's not a mode that is officially supported by the monitor itself, whose data I have decoded below:
EDID version: 1.4
+hsync -vsync
VertFreq: 60.000 Hz, HorFreq: 133.320 kHz
+hsync -vsync
VertFreq: 30.000 Hz, HorFreq: 66.660 kHz
Manufacturer: GSM Model 23305 Serial Number 181370
Made in week 5 of 2016
Digital display
10 bits per primary color channel
DisplayPort interface
Maximum image size: 60 cm x 34 cm
Gamma: 2.20
DPMS levels: Standby
Supported color formats: RGB 4:4:4, YCrCb 4:4:4, YCrCb 4:2:2
Default (sRGB) color space is primary color space
First detailed timing includes the native pixel format and preferred refresh rate
Color Characteristics
Red: 0.6523, 0.3349
Green: 0.3046, 0.6367
Blue: 0.1484, 0.0615
White: 0.3134, 0.3291
Established Timings I & II
640x480 59.940 Hz 4:3 31.469 kHz 25.175 MHz (DMT)
800x600 60.317 Hz 4:3 37.879 kHz 40.000 MHz (DMT)
1024x768 60.004 Hz 4:3 48.363 kHz 65.000 MHz (DMT)
Standard Timings
1152x864 59.959 Hz 4:3 53.783 kHz 81.750 MHz (EDID 1.4 source: CVT)
1152x864 60.000 Hz 4:3 53.700 kHz 81.624 MHz (EDID 1.3 source: GTF)
1280x1024 60.020 Hz 5:4 63.981 kHz 108.000 MHz (DMT)
1280x720 60.000 Hz 16:9 45.000 kHz 74.250 MHz (DMT)
1600x900 60.000 Hz 16:9 60.000 kHz 108.000 MHz (DMT, RB)
1920x1080 60.000 Hz 16:9 67.500 kHz 148.500 MHz (DMT)
1280x800 59.810 Hz 16:10 49.702 kHz 83.500 MHz (DMT)
Detailed mode: Clock 533.280 MHz, 600 mm x 340 mm
3840 3848 3992 4000 ( 8 144 8)
2160 2214 2219 2222 ( 54 5 3)
Detailed mode: Clock 266.640 MHz, 600 mm x 340 mm
3840 3848 3992 4000 ( 8 144 8)
2160 2214 2219 2222 ( 54 5 3)
Display Range Limits
Monitor ranges (GTF): 56-61 Hz V, 30-135 kHz H, max dotclock 560 MHz
Display Product Name: LG Ultra HD
Has 1 extension block
Checksum: 0x11
----------------
CTA-861 Extension Block Revision 3
+hsync +vsync
VertFreq: 60.000 Hz, HorFreq: 67.500 kHz
Basic audio support
Supports YCbCr 4:4:4
Supports YCbCr 4:2:2
1 native detailed modes
13 bytes of CTA data blocks
Video Data Block
1920x1080 60.000 Hz 16:9 67.500 kHz 148.500 MHz (VIC 16, native)
1280x720 60.000 Hz 16:9 45.000 kHz 74.250 MHz (VIC 4)
720x480 59.940 Hz 16:9 31.469 kHz 27.000 MHz (VIC 3)
640x480 59.940 Hz 4:3 31.469 kHz 25.175 MHz (VIC 1)
Audio Data Block
Linear PCM, max channels 2
Supported sample rates (kHz): 48 44.1 32
Supported sample sizes (bits): 24 20 16
Speaker Allocation Data Block
Speaker map:
FL/FR - Front Left/Right
Detailed mode: Clock 148.500 MHz, 600 mm x 340 mm
1920 2008 2052 2200 ( 88 44 148)
1080 1084 1089 1125 ( 4 5 36)
Checksum: 0x41