HDMI output problem with 1024x768 resolution in i.mx8mp

[simon_ko]

I am trying to output HDMI with 1024x768 resolution in i.mx8mp.

The monitor's EDID supports 1024x768 and can be used in 1024x768 when connected to a PC.

Kernel log when HDMI output using i.MX8MP is as follows.

[ 319.904803] [drm:drm_mode_debug_printmodeline] Modeline "1920x1080i": 60 74250 1920 2008 2052 2200 1080 1084 1094 1125 0x40 0x15
[ 319.904809] [drm:drm_mode_prune_invalid] Not using 1920x1080i mode: BAD
[ 319.904818] [drm:drm_mode_debug_printmodeline] Modeline "1440x900": 60 88750 1440 1488 1520 1600 900 903 909 926 0x40 0x9
[ 319.904824] [drm:drm_mode_prune_invalid] Not using 1440x900 mode: CLOCK_RANGE
[ 319.904832] [drm:drm_mode_debug_printmodeline] Modeline "1400x1050": 60 101000 1400 1448 1480 1560 1050 1053 1057 1080 0x40 0x9
[ 319.904838] [drm:drm_mode_prune_invalid] Not using 1400x1050 mode: CLOCK_RANGE
[ 319.904846] [drm:drm_mode_debug_printmodeline] Modeline "640x480": 75 31500 640 656 720 840 480 481 484 500 0x40 0xa
[ 319.904851] [drm:drm_mode_prune_invalid] Not using 640x480 mode: CLOCK_RANGE
[ 319.904860] [drm:drm_mode_debug_printmodeline] Modeline "640x480": 73 31500 640 664 704 832 480 489 492 520 0x40 0xa
[ 319.904865] [drm:drm_mode_prune_invalid] Not using 640x480 mode: CLOCK_RANGE
[ 319.904874] [drm:drm_mode_debug_printmodeline] Modeline "640x480": 67 30240 640 704 768 864 480 483 486 525 0x40 0xa
[ 319.904881] [drm:drm_mode_prune_invalid] Not using 640x480 mode: CLOCK_RANGE
[ 319.904889] [drm:drm_mode_debug_printmodeline] Modeline "720x400": 70 28320 720 738 846 900 400 412 414 449 0x40 0x6
[ 319.904894] [drm:drm_mode_prune_invalid] Not using 720x400 mode: CLOCK_RANGE
[ 319.904903] [drm:drm_mode_debug_printmodeline] Modeline "1024x768": 75 78750 1024 1040 1136 1312 768 769 772 800 0x40 0x5
[ 319.904908] [drm:drm_mode_prune_invalid] Not using 1024x768 mode: CLOCK_RANGE
[ 319.904918] [drm:drm_mode_debug_printmodeline] Modeline "1024x768": 70 75000 1024 1048 1184 1328 768 771 777 806 0x40 0xa
[ 319.904923] [drm:drm_mode_prune_invalid] Not using 1024x768 mode: CLOCK_RANGE
[ 319.904932] [drm:drm_mode_debug_printmodeline] Modeline "1024x768": 60 65000 1024 1048 1184 1344 768 771 777 806 0x60 0xa
[ 319.904937] [drm:drm_mode_prune_invalid] Not using 1024x768 mode: CLOCK_RANGE
[ 319.904945] [drm:drm_mode_debug_printmodeline] Modeline "832x624": 75 57284 832 864 928 1152 624 625 628 667 0x40 0xa
[ 319.904950] [drm:drm_mode_prune_invalid] Not using 832x624 mode: CLOCK_RANGE
[ 319.904959] [drm:drm_mode_debug_printmodeline] Modeline "800x600": 75 49500 800 816 896 1056 600 601 604 625 0x40 0x5
[ 319.904964] [drm:drm_mode_prune_invalid] Not using 800x600 mode: CLOCK_RANGE
[ 319.904973] [drm:drm_mode_debug_printmodeline] Modeline "800x600": 72 50000 800 856 976 1040 600 637 643 666 0x40 0x5
[ 319.904978] [drm:drm_mode_prune_invalid] Not using 800x600 mode: CLOCK_RANGE
[ 319.904986] [drm:drm_mode_debug_printmodeline] Modeline "1920x1080i": 60 74250 1920 2008 2052 2200 1080 1084 1094 1125 0x40 0x15
[ 319.904991] [drm:drm_mode_prune_invalid] Not using 1920x1080i mode: BAD
[ 319.905000] [drm:drm_mode_debug_printmodeline] Modeline "1920x1080i": 50 74250 1920 2448 2492 2640 1080 1084 1094 1125 0x40 0x15
[ 319.905007] [drm:drm_mode_prune_invalid] Not using 1920x1080i mode: BAD
[ 319.905016] [drm:drm_mode_debug_printmodeline] Modeline "1920x1080i": 50 72000 1920 1952 2120 2304 1080 1126 1136 1250 0x40 0x19
[ 319.905020] [drm:drm_mode_prune_invalid] Not using 1920x1080i mode: BAD
[ 319.905030] [drm:drm_mode_debug_printmodeline] Modeline "1920x1080i": 60 74176 1920 2008 2052 2200 1080 1084 1094 1125 0x40 0x15
[ 319.905035] [drm:drm_mode_prune_invalid] Not using 1920x1080i mode: BAD

imx8mp uses drivers/phy/frescale/phy-fsl-samsung-hdmi.c and samsung_phy_pll_cfg does not have setting for 65MHz clock used by 1024x768 @ 60Hz

I want to know how to set the desired resolution and clock.