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I recently got a Waveshare 7" LCD (H) with 3B+, running Raspbian updated to buster (uname -a says Linux rpi33 4.19.42-v7+ #1219 SMP Tue May 14 21:20:58 BST 2019 armv7l GNU/Linux)

I set config.txt according to Waveshare's manual for the product to

max_usb_current=1
hdmi_force_hotplug=1
config_hdmi_boost=7
hdmi_group=2
hdmi_mode=87
hdmi_cvt=1024 600 60 6 0 0 0
# these are testing extras without effect
hdmi_drive=1
hdmi_force_mode=1

and yet, I can't seem to run the display at full resolution; the resolution is lower and there is dark frame around the picture (which makes the touchscreen off, but that is expected).

The extra mode is not listed in /opt/vc/bin/tvservice -m CEA (or -m DMT), /opt/vc/bin/tvservice -s is reporting

state 0x12000a [HDMI CEA (17) RGB lim 4:3], 720x576 @ 50.00Hz, progressive

and xrandr -q reports

Screen 0: minimum 656 x 512, current 656 x 512, maximum 656 x 512

screenshot from mate desktop

EDID from the display (tvservice -d edid.dat; edidparser edid.dat) says

Nothing written!
Enabling fuzzy format match...
Parsing edid.dat...
HDMI:EDID version 1.3, 1 extensions, screen size 41x26 cm
HDMI:EDID features - videodef 0x80 standby suspend active off; colour encoding:RGB444|YCbCr444|YCbCr422; sRGB is default colourspace; preferred format is native; does not support GTF
HDMI:EDID found monitor name descriptor tag 0xfc
HDMI:EDID monitor name is LEN_L1950wD
HDMI:EDID found monitor range descriptor tag 0xfd
HDMI:EDID monitor range offsets: V min=0, V max=0, H min=0, H max=0
HDMI:EDID monitor range: vertical is 50-76 Hz, horizontal is 30-81 kHz, max pixel clock is 140 MHz
HDMI:EDID monitor range does not support GTF
HDMI:EDID found monitor S/N descriptor tag 0xff
HDMI:EDID failed to find a matching detail format for 1024x600p hfp:5 hs:13 hbp:270 vfp:2 vs:3 vbp:17 pixel clock:49 MHz
HDMI:EDID calculated refresh rate is 60 Hz
HDMI:EDID guessing the format to be 1024x600p @60 Hz
HDMI:EDID found unknown detail timing format: 1024x600p hfp:5 hs:13 hbp:270 vfp:2 vs:3 vbp:17 pixel clock:49 MHz
HDMI:EDID established timing I/II bytes are AF EF 00
HDMI:EDID found DMT format: code 4, 640x480p @ 60 Hz in established timing I/II
HDMI:EDID found DMT format: code 5, 640x480p @ 72 Hz in established timing I/II
HDMI:EDID found DMT format: code 6, 640x480p @ 75 Hz in established timing I/II
HDMI:EDID found DMT format: code 8, 800x600p @ 56 Hz in established timing I/II
HDMI:EDID found DMT format: code 9, 800x600p @ 60 Hz in established timing I/II
HDMI:EDID found DMT format: code 10, 800x600p @ 72 Hz in established timing I/II
HDMI:EDID found DMT format: code 11, 800x600p @ 75 Hz in established timing I/II
HDMI:EDID found DMT format: code 16, 1024x768p @ 60 Hz in established timing I/II
HDMI:EDID found DMT format: code 17, 1024x768p @ 70 Hz in established timing I/II
HDMI:EDID found DMT format: code 18, 1024x768p @ 75 Hz in established timing I/II
HDMI:EDID found DMT format: code 36, 1280x1024p @ 75 Hz in established timing I/II
HDMI:EDID standard timings block x 8: 0x714F 81C0 8180 8180 8180 9500 950F D1C0 
HDMI:EDID found DMT format: code 21, 1152x864p @ 75 Hz (4:3) in standard timing 0
HDMI:EDID found DMT format: code 85, 1280x720p @ 60 Hz (16:9) in standard timing 1
HDMI:EDID found DMT format: code 35, 1280x1024p @ 60 Hz (5:4) in standard timing 2
HDMI:EDID found DMT format: code 35, 1280x1024p @ 60 Hz (5:4) in standard timing 3
HDMI:EDID found DMT format: code 35, 1280x1024p @ 60 Hz (5:4) in standard timing 4
HDMI:EDID found DMT format: code 47, 1440x900p @ 60 Hz (16:10) in standard timing 5
HDMI:EDID found DMT format: code 48, 1440x900p @ 75 Hz (16:10) in standard timing 6
HDMI:EDID found DMT format: code 82, 1920x1080p @ 60 Hz (16:9) in standard timing 7
HDMI:EDID parsing v3 CEA extension 0
HDMI:EDID monitor support - underscan IT formats:no, basic audio:yes, yuv444:yes, yuv422:yes, #native DTD:1
HDMI:EDID found preferred CEA detail timing format: 720x576p @ 50 Hz (17)
HDMI:EDID found CEA detail timing format: 1920x1080i @ 60 Hz (5)
HDMI:EDID found CEA detail timing format: 1920x1080i @ 50 Hz (20)
HDMI:EDID found CEA detail timing format: 1280x720p @ 50 Hz (19)
HDMI:EDID found CEA detail timing format: 1920x1080p @ 50 Hz (31)
HDMI:EDID found CEA format: code 6, 1440x480i @ 60Hz 
HDMI:EDID found CEA format: code 7, 1440x480i @ 60Hz 
HDMI:EDID found CEA format: code 2, 720x480p @ 60Hz 
HDMI:EDID found CEA format: code 3, 720x480p @ 60Hz 
HDMI:EDID found CEA format: code 21, 1440x576i @ 50Hz 
HDMI:EDID found CEA format: code 22, 1440x576i @ 50Hz (native)
HDMI:EDID found CEA format: code 17, 720x576p @ 50Hz 
HDMI:EDID found CEA format: code 18, 720x576p @ 50Hz 
HDMI:EDID found CEA format: code 19, 1280x720p @ 50Hz 
HDMI:EDID found CEA format: code 4, 1280x720p @ 60Hz 
HDMI:EDID found CEA format: code 20, 1920x1080i @ 50Hz 
HDMI:EDID found CEA format: code 5, 1920x1080i @ 60Hz 
HDMI:EDID found CEA format: code 31, 1920x1080p @ 50Hz 
HDMI:EDID found CEA format: code 16, 1920x1080p @ 60Hz (native)
HDMI:EDID found audio format 2 channels PCM, sample rate: 32|44|48 kHz, sample size: 16|20|24 bits
HDMI:EDID found HDMI VSDB length 5
HDMI:EDID HDMI VSDB has physical address 1.0.0.0
HDMI:EDID HDMI VSDB has no extension fields
HDMI:EDID adding mandatory support for CEA (1) 640x480p @ 60Hz
HDMI:EDID filtering formats with pixel clock > 162 MHz or h. blanking > 1023
HDMI:EDID best score mode initialised to CEA (1) 640x480p @ 60 Hz with pixel clock 25 MHz (score 0)
HDMI:EDID best score mode is now CEA (1) 640x480p @ 60 Hz with pixel clock 25 MHz (score 61864)
HDMI:EDID best score mode is now CEA (2) 720x480p @ 60 Hz with pixel clock 27 MHz (score 66472)
HDMI:EDID CEA mode (3) 720x480p @ 60 Hz with pixel clock 27 MHz has a score of 66472
HDMI:EDID best score mode is now CEA (4) 1280x720p @ 60 Hz with pixel clock 74 MHz (score 135592)
HDMI:EDID DMT mode (4) 640x480p @ 60 Hz with pixel clock 25 MHz has a score of 18432
HDMI:EDID best score mode is now CEA (5) 1920x1080i @ 60 Hz with pixel clock 74 MHz (score 4773832)
HDMI:EDID DMT mode (5) 640x480p @ 72 Hz with pixel clock 31 MHz has a score of 22118
HDMI:EDID CEA mode (6) 1440x480i @ 60 Hz with pixel clock 27 MHz has a score of 45736
HDMI:EDID DMT mode (6) 640x480p @ 75 Hz with pixel clock 31 MHz has a score of 23040
HDMI:EDID CEA mode (7) 1440x480i @ 60 Hz with pixel clock 27 MHz has a score of 45736
HDMI:EDID DMT mode (8) 800x600p @ 56 Hz with pixel clock 36 MHz has a score of 26880
HDMI:EDID DMT mode (9) 800x600p @ 60 Hz with pixel clock 40 MHz has a score of 28800
HDMI:EDID DMT mode (10) 800x600p @ 72 Hz with pixel clock 50 MHz has a score of 34560
HDMI:EDID DMT mode (11) 800x600p @ 75 Hz with pixel clock 49 MHz has a score of 36000
HDMI:EDID CEA mode (16) 1920x1080p @ 60 Hz with pixel clock 148 MHz has a score of 398248
HDMI:EDID DMT mode (16) 1024x768p @ 60 Hz with pixel clock 65 MHz has a score of 47185
HDMI:EDID best score mode is now CEA (17) 720x576p @ 50 Hz with pixel clock 27 MHz (score 5087208)
HDMI:EDID DMT mode (17) 1024x768p @ 70 Hz with pixel clock 75 MHz has a score of 55050
HDMI:EDID CEA mode (18) 720x576p @ 50 Hz with pixel clock 27 MHz has a score of 66472
HDMI:EDID DMT mode (18) 1024x768p @ 75 Hz with pixel clock 78 MHz has a score of 58982
HDMI:EDID CEA mode (19) 1280x720p @ 50 Hz with pixel clock 74 MHz has a score of 3617160
HDMI:EDID CEA mode (20) 1920x1080i @ 50 Hz with pixel clock 74 MHz has a score of 4232360
HDMI:EDID CEA mode (21) 1440x576i @ 50 Hz with pixel clock 27 MHz has a score of 45736
HDMI:EDID DMT mode (21) 1152x864p @ 75 Hz with pixel clock 108 MHz has a score of 99649
HDMI:EDID CEA mode (22) 1440x576i @ 50 Hz with pixel clock 27 MHz has a score of 56104
HDMI:EDID CEA mode (31) 1920x1080p @ 50 Hz with pixel clock 148 MHz has a score of 3232360
HDMI:EDID DMT mode (35) 1280x1024p @ 60 Hz with pixel clock 108 MHz has a score of 103643
HDMI:EDID DMT mode (36) 1280x1024p @ 75 Hz with pixel clock 135 MHz has a score of 98304
HDMI:EDID DMT mode (47) 1440x900p @ 60 Hz with pixel clock 106 MHz has a score of 102760
HDMI:EDID DMT mode (48) 1440x900p @ 75 Hz with pixel clock 136 MHz has a score of 122200
HDMI:EDID DMT mode (82) 1920x1080p @ 60 Hz with pixel clock 148 MHz has a score of 149416
HDMI:EDID DMT mode (85) 1280x720p @ 60 Hz with pixel clock 74 MHz has a score of 80296
HDMI:EDID preferred mode remained as CEA (17) 720x576p @ 50 Hz with pixel clock 27 MHz
HDMI:EDID has HDMI support and audio support
edidparser exited with code 0

Is this fixable without much sorcery? Thanks!

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FWIW, all this was fixed by running raspi-config/Advanced/GL Driver/GL (Full KMS) and rebooting. I could also remove everything from config.txt and the display gets detected and used.

screenshot at full resolution

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