mmc: sdhci-esdhc-imx: explicitly reset tuning circuit via RSTT bit

According to the i.MX Reference Manual, the RSTT bit (SYS_CTRL[28]) is
designed to reset the tuning circuit. While the Reference Manual states
that clearing EXECUTE_TUNING bit from 1 to 0 in AUTOCMD12_ERR_STATUS
can also set RSTT, this mechanism only works when the original
EXECUTE_TUNING bit was 1. When the bit is already 0, the tuning circuit
reset will not be triggered.

This explicit reset approach strengthens the tuning reliability and
aligns with the Reference Manual recommendations.

Signed-off-by: Haibo Chen <[email protected]>
Signed-off-by: Luke Wang <[email protected]>
Acked-by: Adrian Hunter <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Ulf Hansson <[email protected]>

Author: Haibo Chen

drivers/mmc/host/sdhci-esdhc-imx.c

@@ -32,6 +32,7 @@
 
 #define ESDHC_SYS_CTRL_DTOCV_MASK	GENMASK(19, 16)
 #define ESDHC_SYS_CTRL_IPP_RST_N	BIT(23)
+#define ESDHC_SYS_CTRL_RESET_TUNING	BIT(28)
 #define	ESDHC_CTRL_D3CD			0x08
 #define ESDHC_BURST_LEN_EN_INCR		(1 << 27)
 /* VENDOR SPEC register */
@@ -1065,7 +1066,7 @@ static void esdhc_reset_tuning(struct sdhci_host *host)
 {
 	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
 	struct pltfm_imx_data *imx_data = sdhci_pltfm_priv(pltfm_host);
-	u32 ctrl, tuning_ctrl;
+	u32 ctrl, tuning_ctrl, sys_ctrl;
 	int ret;
 
 	/* Reset the tuning circuit */
@@ -1089,6 +1090,11 @@ static void esdhc_reset_tuning(struct sdhci_host *host)
 				writel(tuning_ctrl, host->ioaddr + ESDHC_TUNING_CTRL);
 			}
 
+			/* set the reset tuning bit */
+			sys_ctrl = readl(host->ioaddr + ESDHC_SYSTEM_CONTROL);
+			sys_ctrl |= ESDHC_SYS_CTRL_RESET_TUNING;
+			writel(sys_ctrl, host->ioaddr + ESDHC_SYSTEM_CONTROL);
+
 			ctrl = readl(host->ioaddr + SDHCI_AUTO_CMD_STATUS);
 			ctrl &= ~ESDHC_MIX_CTRL_SMPCLK_SEL;
 			ctrl &= ~ESDHC_MIX_CTRL_EXE_TUNE;