[PATCH v8 4/4] riscv: dts: thead: Enable LicheePi 4A eMMC and microSD

[Maxim Kiselev]

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