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

[Xi Ruoyao]

On Wed, 2024-03-20 at 15:28 +0300, Maxim Kiselev wrote:
> 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?

I'll try it this weekend.  Now having some work with "real time
priority" to do :(.

-- 
Xi Ruoyao <xry111 at xry111.site>
School of Aerospace Science and Technology, Xidian University