[Samsung Galaxy S8 & S8+ Cross Device Development] rostifaner:
@ace2nutzer

Flashed your test kernel then reboot 2 times and I get this output

dreamlte:/ # cat /proc/last_kmsg | grep "mmc_host mmc0"
<6>mmc_host mmc0: Bus speed (slot 0) = 25000000Hz (slot req 400000Hz, actual 390625HZ div = 32)
<6>mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 200000000Hz, actual 200000000HZ div = 0)
<6>mmc_host mmc0: Tuning error: cmd.error:-5, data.error:-115 CLKSEL = 0x03030003, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030044, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030004, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Bus speed (slot 0) = 25000000Hz (slot req 400000Hz, actual 390625HZ div = 32)
<6>mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 200000000Hz, actual 200000000HZ div = 0)
<6>mmc_host mmc0: Tuning error: cmd.error:-5, data.error:-115 CLKSEL = 0x03030003, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030044, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030004, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Bus speed (slot 0) = 25000000Hz (slot req 400000Hz, actual 390625HZ div = 32)
<6>mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 200000000Hz, actual 200000000HZ div = 0)
<6>mmc_host mmc0: Tuning error: cmd.error:-5, data.error:-115 CLKSEL = 0x03030003, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030044, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030004, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Bus speed (slot 0) = 25000000Hz (slot req 400000Hz, actual 390625HZ div = 32)
<6>mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 200000000Hz, actual 200000000HZ div = 0)
<6>mmc_host mmc0: Tuning error: cmd.error:-5, data.error:-115 CLKSEL = 0x03030003, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030044, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030004, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Bus speed (slot 0) = 25000000Hz (slot req 400000Hz, actual 390625HZ div = 32)
<6>mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 200000000Hz, actual 200000000HZ div = 0)
<6>mmc_host mmc0: Tuning error: cmd.error:-5, data.error:-115 CLKSEL = 0x03030003, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030044, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030004, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Bus speed (slot 0) = 25000000Hz (slot req 400000Hz, actual 390625HZ div = 32)
<6>mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 200000000Hz, actual 200000000HZ div = 0)
<6>mmc_host mmc0: Tuning error: cmd.error:-5, data.error:-115 CLKSEL = 0x03030003, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030044, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030004, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Bus speed (slot 0) = 25000000Hz (slot req 400000Hz, actual 390625HZ div = 32)
<6>mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 200000000Hz, actual 200000000HZ div = 0)
<6>mmc_host mmc0: Tuning error: cmd.error:-5, data.error:-115 CLKSEL = 0x03030003, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030044, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030004, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: card inserted
<6>mmc_host mmc0: Bus speed (slot 0) = 25000000Hz (slot req 400000Hz, actual 390625HZ div = 32)
<6>mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 200000000Hz, actual 200000000HZ div = 0)
<6>mmc_host mmc0: Tuning error: cmd.error:-5, data.error:-115 CLKSEL = 0x03030043, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:-5, data.error:-115 CLKSEL = 0x03030003, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030044, EN_SHIFT = 0x00000000
<6>mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030004, EN_SHIFT = 0x00000000

But its strange for me also, Im using your kernel more than 1 year and got strange behaviour with random reboots after 06112020 version, as I remember int_freq has changed much earlier(maybe im wrong). So the last stable version for me its 27092020 and according to your git commit maybe its ram issue due to defconfigs: disable PGTABLE_MAPPING(Just my guesses).

UPD

Flashed your stock kernel and have same output

dreamlte:/ # cat /proc/last_kmsg | grep "mmc_host mmc0"
<6>[ 1.082106] [0: kworker/0:1: 1299] mmc_host mmc0: card inserted
<6>[ 1.112109] [7: kworker/u16:2: 53] mmc_host mmc0: Bus speed (slot 0) = 25000000Hz (slot req 400000Hz, actual 390625HZ div = 32)
<6>[ 1.329442] [5: kworker/u16:2: 53] mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 200000000Hz, actual 200000000HZ div = 0)
<6>[ 1.329979] [4: kworker/u16:2: 53] mmc_host mmc0: Tuning error: cmd.error:-5, data.error:-115 CLKSEL = 0x03030043, EN_SHIFT = 0x00000000
<6>[ 1.330075] [4: kworker/u16:2: 53] mmc_host mmc0: Tuning error: cmd.error:-5, data.error:-115 CLKSEL = 0x03030003, EN_SHIFT = 0x00000000
<6>[ 1.330225] [4: kworker/u16:2: 53] mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030044, EN_SHIFT = 0x00000000
<6>[ 1.330352] [5: kworker/u16:2: 53] mmc_host mmc0: Tuning error: cmd.error:0, data.error:-84 CLKSEL = 0x03030004, EN_SHIFT = 0x00000000

UPD2

Also maybe its rom issues? soon Im going to install latest( G950FXXSBDUA3 ) version and see what happens with your last kernel