mmc: tegra: Write xfer_mode, CMD regs in together

If there is a gap between xfer mode and command register writes,
tegra SDMMC controller can sometimes issue a spurious command before
the CMD register is written. To avoid this, these two registers need
to be written together in a single write operation.

This is implemented as an NVQUIRK as it applies to T114, T124 and
T132.

Signed-off-by: Pavan Kunapuli <pkunapuli@nvidia.com>
Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci-tegra.c

@@ -41,6 +41,7 @@
 #define NVQUIRK_DISABLE_SDR50		BIT(3)
 #define NVQUIRK_DISABLE_SDR104		BIT(4)
 #define NVQUIRK_DISABLE_DDR50		BIT(5)
+#define NVQUIRK_SHADOW_XFER_MODE_REG	BIT(6)
 
 struct sdhci_tegra_soc_data {
 	const struct sdhci_pltfm_data *pdata;
@@ -67,6 +68,31 @@ static u16 tegra_sdhci_readw(struct sdhci_host *host, int reg)
 	return readw(host->ioaddr + reg);
 }
 
+static void tegra_sdhci_writew(struct sdhci_host *host, u16 val, int reg)
+{
+	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
+	struct sdhci_tegra *tegra_host = pltfm_host->priv;
+	const struct sdhci_tegra_soc_data *soc_data = tegra_host->soc_data;
+
+	if (soc_data->nvquirks & NVQUIRK_SHADOW_XFER_MODE_REG) {
+		switch (reg) {
+		case SDHCI_TRANSFER_MODE:
+			/*
+			 * Postpone this write, we must do it together with a
+			 * command write that is down below.
+			 */
+			pltfm_host->xfer_mode_shadow = val;
+			return;
+		case SDHCI_COMMAND:
+			writel((val << 16) | pltfm_host->xfer_mode_shadow,
+				host->ioaddr + SDHCI_TRANSFER_MODE);
+			return;
+		}
+	}
+
+	writew(val, host->ioaddr + reg);
+}
+
 static void tegra_sdhci_writel(struct sdhci_host *host, u32 val, int reg)
 {
 	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
@@ -147,6 +173,7 @@ static void tegra_sdhci_set_bus_width(struct sdhci_host *host, int bus_width)
 static const struct sdhci_ops tegra_sdhci_ops = {
 	.get_ro     = tegra_sdhci_get_ro,
 	.read_w     = tegra_sdhci_readw,
+	.write_w    = tegra_sdhci_writew,
 	.write_l    = tegra_sdhci_writel,
 	.set_clock  = sdhci_set_clock,
 	.set_bus_width = tegra_sdhci_set_bus_width,
@@ -201,7 +228,8 @@ static struct sdhci_tegra_soc_data soc_data_tegra114 = {
 	.pdata = &sdhci_tegra114_pdata,
 	.nvquirks = NVQUIRK_DISABLE_SDR50 |
 		    NVQUIRK_DISABLE_DDR50 |
-		    NVQUIRK_DISABLE_SDR104,
+		    NVQUIRK_DISABLE_SDR104 |
+		    NVQUIRK_SHADOW_XFER_MODE_REG,
 };
 
 static const struct of_device_id sdhci_tegra_dt_match[] = {