When using the latest Linaro Snapshots based on linux 5.7 (5.7.19-00177-g4af49ea41ecf-127) on the db820c, the SD card slot fails. Here are the error messages:
[ 44.798424] mmc0: Timeout waiting for hardware interrupt.
[ 44.798461] mmc0: sdhci: ============ SDHCI REGISTER DUMP ===========
[ 44.802803] mmc0: sdhci: Sys addr: 0x00000000 | Version: 0x00004902
[ 44.809229] mmc0: sdhci: Blk size: 0x00004008 | Blk cnt: 0x00000000
[ 44.815665] mmc0: sdhci: Argument: 0x00000000 | Trn mode: 0x00000013
[ 44.822072] mmc0: sdhci: Present: 0x03f80206 | Host ctl: 0x00000019
[ 44.828496] mmc0: sdhci: Power: 0x00000001 | Blk gap: 0x00000000
[ 44.834920] mmc0: sdhci: Wake-up: 0x00000000 | Clock: 0x00000007
[ 44.841343] mmc0: sdhci: Timeout: 0x0000000a | Int stat: 0x00000000
[ 44.847765] mmc0: sdhci: Int enab: 0x03ff900b | Sig enab: 0x03ff100b
[ 44.854190] mmc0: sdhci: ACmd stat: 0x00000000 | Slot int: 0x00000000
[ 44.860613] mmc0: sdhci: Caps: 0x322dc8b2 | Caps_1: 0x00008007
[ 44.867037] mmc0: sdhci: Cmd: 0x0000333a | Max curr: 0x00000000
[ 44.873460] mmc0: sdhci: Resp[0]: 0x00000920 | Resp[1]: 0x5b590000
[ 44.879884] mmc0: sdhci: Resp[2]: 0x76b27f80 | Resp[3]: 0x0a404012
[ 44.886307] mmc0: sdhci: Host ctl2: 0x00000008
[ 44.892728] mmc0: sdhci: ADMA Err: 0x00000000 | ADMA Ptr: 0x000000017830a200
[ 44.897071] mmc0: sdhci: ============================================
[ 45.004351] mmc0: Reset 0x4 never completed.
[ 45.004373] mmc0: sdhci: ============ SDHCI REGISTER DUMP ===========
[ 45.007680] mmc0: sdhci: Sys addr: 0x00000000 | Version: 0x00004902
[ 45.014016] mmc0: sdhci: Blk size: 0x00004008 | Blk cnt: 0x00000000
[ 45.020439] mmc0: sdhci: Argument: 0x00000000 | Trn mode: 0x00000013
[ 45.026862] mmc0: sdhci: Present: 0x03f80206 | Host ctl: 0x00000019
[ 45.033286] mmc0: sdhci: Power: 0x00000001 | Blk gap: 0x00000000
[ 45.039711] mmc0: sdhci: Wake-up: 0x00000000 | Clock: 0x00000007
[ 45.046133] mmc0: sdhci: Timeout: 0x0000000a | Int stat: 0x00000000
[ 45.052556] mmc0: sdhci: Int enab: 0x03ff900b | Sig enab: 0x03ff100b
[ 45.058981] mmc0: sdhci: ACmd stat: 0x00000000 | Slot int: 0x00000000
[ 45.065404] mmc0: sdhci: Caps: 0x322dc8b2 | Caps_1: 0x00008007
[ 45.071828] mmc0: sdhci: Cmd: 0x0000333a | Max curr: 0x00000000
[ 45.078252] mmc0: sdhci: Resp[0]: 0x00000000 | Resp[1]: 0x00000000
[ 45.084675] mmc0: sdhci: Resp[2]: 0x00000000 | Resp[3]: 0x00000000
[ 45.091097] mmc0: sdhci: Host ctl2: 0x00000008
[ 45.097518] mmc0: sdhci: ADMA Err: 0x00000000 | ADMA Ptr: 0x000000017830a200
[ 45.101863] mmc0: sdhci: ============================================
[ 45.109768] mmc0: error -110 whilst initialising SD card
[ 45.216309] mmc0: Reset 0x4 never completed.
[ 45.216430] mmc0: sdhci: ============ SDHCI REGISTER DUMP ===========
[ 45.219751] mmc0: sdhci: Sys addr: 0x00000000 | Version: 0x00004902
[ 45.226085] mmc0: sdhci: Blk size: 0x00004008 | Blk cnt: 0x00000000
[ 45.232507] mmc0: sdhci: Argument: 0x00000000 | Trn mode: 0x00000013
[ 45.238932] mmc0: sdhci: Present: 0x03f80206 | Host ctl: 0x00000019
[ 45.245354] mmc0: sdhci: Power: 0x00000001 | Blk gap: 0x00000000
[ 45.251778] mmc0: sdhci: Wake-up: 0x00000000 | Clock: 0x00000007
[ 45.258202] mmc0: sdhci: Timeout: 0x0000000a | Int stat: 0x00000000
[ 45.264625] mmc0: sdhci: Int enab: 0x03ff900b | Sig enab: 0x03ff100b
[ 45.271048] mmc0: sdhci: ACmd stat: 0x00000000 | Slot int: 0x00000000
[ 45.277473] mmc0: sdhci: Caps: 0x322dc8b2 | Caps_1: 0x00008007
[ 45.283896] mmc0: sdhci: Cmd: 0x00000102 | Max curr: 0x00000000
[ 45.290319] mmc0: sdhci: Resp[0]: 0x00000000 | Resp[1]: 0x00000000
[ 45.296743] mmc0: sdhci: Resp[2]: 0x00000000 | Resp[3]: 0x00000000
[ 45.303165] mmc0: sdhci: Host ctl2: 0x00000008
[ 45.309572] mmc0: sdhci: ADMA Err: 0x00000000 | ADMA Ptr: 0x000000017830a200
[ 45.313933] mmc0: sdhci: ============================================
[ 45.421686] mmc0: Reset 0x1 never completed.
[ 45.421715] mmc0: sdhci: ============ SDHCI REGISTER DUMP ===========
[ 45.425045] mmc0: sdhci: Sys addr: 0x00000000 | Version: 0x00004902
[ 45.431383] mmc0: sdhci: Blk size: 0x00004008 | Blk cnt: 0x00000000
[ 45.437805] mmc0: sdhci: Argument: 0x00000000 | Trn mode: 0x00000013
[ 45.444225] mmc0: sdhci: Present: 0x03f80206 | Host ctl: 0x00000018
[ 45.450646] mmc0: sdhci: Power: 0x00000001 | Blk gap: 0x00000000
[ 45.457079] mmc0: sdhci: Wake-up: 0x00000000 | Clock: 0x00000007
[ 45.463631] mmc0: sdhci: Timeout: 0x0000000a | Int stat: 0x00000000
[ 45.469926] mmc0: sdhci: Int enab: 0x03ff900b | Sig enab: 0x00000000
[ 45.476342] mmc0: sdhci: ACmd stat: 0x00000000 | Slot int: 0x00000000
[ 45.482939] mmc0: sdhci: Caps: 0x322dc8b2 | Caps_1: 0x00008007
[ 45.489205] mmc0: sdhci: Cmd: 0x00000102 | Max curr: 0x00000000
[ 45.495629] mmc0: sdhci: Resp[0]: 0x00000000 | Resp[1]: 0x00000000
[ 45.502035] mmc0: sdhci: Resp[2]: 0x00000000 | Resp[3]: 0x00000000
[ 45.508460] mmc0: sdhci: Host ctl2: 0x00000008
[ 45.514879] mmc0: sdhci: ADMA Err: 0x00000000 | ADMA Ptr: 0x000000017830a200
[ 45.519728] mmc0: sdhci: ============================================