mmc: sdhci-tegra: enforce min window size for manual tuning

Check against minimum allowed sampling window size on manual tuning.
That allows DDR200 to fail if not enough and then re-init to SDR104.
A safe window size for DDR200 is 8.

drivers/mmc/host/sdhci-tegra.c

@@ -1663,6 +1663,7 @@ static void tegra_sdhci_execute_manual_tuning(struct sdhci_host *host, int num_i
 }
 
 #define INVALID_TAP 0x100
+#define SAMPLING_WINDOW_SIZE_MIN 8 /* DDR200 */
 static int tegra_sdhci_execute_tuning_ddr200(struct sdhci_host *host)
 {
 	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
@@ -1730,6 +1731,15 @@ static int tegra_sdhci_execute_tuning_ddr200(struct sdhci_host *host)
 		}
 	}
 
+	if (best_size < SAMPLING_WINDOW_SIZE_MIN) {
+		dev_err(mmc_dev(host->mmc),
+			"manual tuning failed, "
+			"sampling window size (%d) too small...\n",
+			best_size);
+		err = -EIO;
+		goto out;
+	}
+
 	if (!best_tap) {
 		dev_err(mmc_dev(host->mmc),
 			"manual tuning failed, no best tap...\n");