Hi Xi, Drew I have the same problem with SD on my LicheePi 4A. After some investigations I found how to fix this tuning error. Here is the patch that increases tuning loop count from 40(MAX_TUNING_LOOP at sdhci.c) to 128. diff --git a/drivers/mmc/host/sdhci-of-dwcmshc.c b/drivers/mmc/host/sdhci-of-dwcmshc.c index 8d6cfb648096..da8f5820fb69 100644 --- a/drivers/mmc/host/sdhci-of-dwcmshc.c +++ b/drivers/mmc/host/sdhci-of-dwcmshc.c @@ -706,6 +706,7 @@ static int th1520_execute_tuning(struct sdhci_host *host, u32 opcode) /* perform tuning */ sdhci_start_tuning(host); + host->tuning_loop_count = 128: host->tuning_err = __sdhci_execute_tuning(host, opcode); if (host->tuning_err) { /* disable auto-tuning upon tuning error */ After that change tuning works fine. The same value of loop count is used in RevyOS BSP https://github.com/revyos/thead-kernel/blob/c6d4e5df18a17903d012ffd89e67d0ee5ce6cf2d/drivers/mmc/host/sdhci-of-dwcmshc.c#L185 Honestly, it looks a little bit strange for me. It seems that the tuning algorithm requires to move through all the taps of delay line(128 taps?) even if we use THRESHOLD_MODE instend LARGEST_WIN_MODE (I mean bit 2 in AT_CTRL_R(0x540) register). Xi, could you also test my fix on your board? Best regards, Maksim