mmc: sdhci-esdhc-imx: Fix DAT line software reset

On i.MX25, the eSDHC DAT line software reset (SYSCTL.RSTD) unexpectedly
clears at least the data transfer width (PROCTL.DTW), which then results
in data CRC errors. This behavior is not documented, but it has actually
been observed. Consequently, the DAT line software resets triggered by
sdhci.c in case of errors caused unrecoverable errors.

Fix this by making sure that the DAT line software reset does not alter
the Host Control register. This behavior being undocumented, it may also
be present on other i.MX SoCs, so apply this fix for the whole i.MX
family.
Signed-off-by: Benoît Thébaudeau <benoit@wsystem.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

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

@@ -579,7 +579,7 @@ static void esdhc_writeb_le(struct sdhci_host *host, u8 val, int reg)
 {
 	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
 	struct pltfm_imx_data *imx_data = sdhci_pltfm_priv(pltfm_host);
-	u32 new_val;
+	u32 new_val = 0;
 	u32 mask;
 
 	switch (reg) {
@@ -610,29 +610,46 @@ static void esdhc_writeb_le(struct sdhci_host *host, u8 val, int reg)
 
 		esdhc_clrset_le(host, mask, new_val, reg);
 		return;
+	case SDHCI_SOFTWARE_RESET:
+		if (val & SDHCI_RESET_DATA)
+			new_val = readl(host->ioaddr + SDHCI_HOST_CONTROL);
+		break;
 	}
 	esdhc_clrset_le(host, 0xff, val, reg);
 
-	/*
-	 * The esdhc has a design violation to SDHC spec which tells
-	 * that software reset should not affect card detection circuit.
-	 * But esdhc clears its SYSCTL register bits [0..2] during the
-	 * software reset.  This will stop those clocks that card detection
-	 * circuit relies on.  To work around it, we turn the clocks on back
-	 * to keep card detection circuit functional.
-	 */
-	if ((reg == SDHCI_SOFTWARE_RESET) && (val & 1)) {
-		esdhc_clrset_le(host, 0x7, 0x7, ESDHC_SYSTEM_CONTROL);
-		/*
-		 * The reset on usdhc fails to clear MIX_CTRL register.
-		 * Do it manually here.
-		 */
-		if (esdhc_is_usdhc(imx_data)) {
-			/* the tuning bits should be kept during reset */
-			new_val = readl(host->ioaddr + ESDHC_MIX_CTRL);
-			writel(new_val & ESDHC_MIX_CTRL_TUNING_MASK,
-					host->ioaddr + ESDHC_MIX_CTRL);
-			imx_data->is_ddr = 0;
+	if (reg == SDHCI_SOFTWARE_RESET) {
+		if (val & SDHCI_RESET_ALL) {
+			/*
+			 * The esdhc has a design violation to SDHC spec which
+			 * tells that software reset should not affect card
+			 * detection circuit. But esdhc clears its SYSCTL
+			 * register bits [0..2] during the software reset. This
+			 * will stop those clocks that card detection circuit
+			 * relies on. To work around it, we turn the clocks on
+			 * back to keep card detection circuit functional.
+			 */
+			esdhc_clrset_le(host, 0x7, 0x7, ESDHC_SYSTEM_CONTROL);
+			/*
+			 * The reset on usdhc fails to clear MIX_CTRL register.
+			 * Do it manually here.
+			 */
+			if (esdhc_is_usdhc(imx_data)) {
+				/*
+				 * the tuning bits should be kept during reset
+				 */
+				new_val = readl(host->ioaddr + ESDHC_MIX_CTRL);
+				writel(new_val & ESDHC_MIX_CTRL_TUNING_MASK,
+						host->ioaddr + ESDHC_MIX_CTRL);
+				imx_data->is_ddr = 0;
+			}
+		} else if (val & SDHCI_RESET_DATA) {
+			/*
+			 * The eSDHC DAT line software reset clears at least the
+			 * data transfer width on i.MX25, so make sure that the
+			 * Host Control register is unaffected.
+			 */
+			esdhc_clrset_le(host, 0xff, new_val,
+					SDHCI_HOST_CONTROL);
 		}
 	}
 }