diff --git a/arch/avr32/boards/atngw100/setup.c b/arch/avr32/boards/atngw100/setup.c
index b8286f1ce854..f3085208959f 100644
--- a/arch/avr32/boards/atngw100/setup.c
+++ b/arch/avr32/boards/atngw100/setup.c
@@ -53,8 +53,11 @@ static struct spi_board_info spi0_board_info[] __initdata = {
 };
 
 static struct mci_platform_data __initdata mci0_data = {
-	.detect_pin	= GPIO_PIN_PC(25),
-	.wp_pin		= GPIO_PIN_PE(0),
+	.slot[0] = {
+		.bus_width	= 4,
+		.detect_pin	= GPIO_PIN_PC(25),
+		.wp_pin		= GPIO_PIN_PE(0),
+	},
 };
 
 /*
diff --git a/arch/avr32/boards/atstk1000/atstk1002.c b/arch/avr32/boards/atstk1000/atstk1002.c
index dfc3443e23aa..4fedbc4488de 100644
--- a/arch/avr32/boards/atstk1000/atstk1002.c
+++ b/arch/avr32/boards/atstk1000/atstk1002.c
@@ -264,16 +264,20 @@ void __init setup_board(void)
 
 #ifndef CONFIG_BOARD_ATSTK100X_SW2_CUSTOM
 
+static struct mci_platform_data __initdata mci0_data = {
+	.slot[0] = {
+		.bus_width	= 4,
+
 /* MMC card detect requires MACB0 *NOT* be used */
 #ifdef CONFIG_BOARD_ATSTK1002_SW6_CUSTOM
-static struct mci_platform_data __initdata mci0_data = {
-	.detect_pin	= GPIO_PIN_PC(14),	/* gpio30/sdcd */
-	.wp_pin		= GPIO_PIN_PC(15),	/* gpio31/sdwp */
-};
-#define MCI_PDATA	&mci0_data
+		.detect_pin	= GPIO_PIN_PC(14), /* gpio30/sdcd */
+		.wp_pin		= GPIO_PIN_PC(15), /* gpio31/sdwp */
 #else
-#define MCI_PDATA	NULL
+		.detect_pin	= -ENODEV,
+		.wp_pin		= -ENODEV,
 #endif	/* SW6 for sd{cd,wp} routing */
+	},
+};
 
 #endif	/* SW2 for MMC signal routing */
 
@@ -326,7 +330,7 @@ static int __init atstk1002_init(void)
 	at32_add_device_spi(1, spi1_board_info, ARRAY_SIZE(spi1_board_info));
 #endif
 #ifndef CONFIG_BOARD_ATSTK100X_SW2_CUSTOM
-	at32_add_device_mci(0, MCI_PDATA);
+	at32_add_device_mci(0, &mci0_pdata);
 #endif
 #ifdef CONFIG_BOARD_ATSTK1002_SW5_CUSTOM
 	set_hw_addr(at32_add_device_eth(1, &eth_data[1]));
diff --git a/arch/avr32/boards/atstk1000/atstk1003.c b/arch/avr32/boards/atstk1000/atstk1003.c
index 0cf664174c17..acc61235b895 100644
--- a/arch/avr32/boards/atstk1000/atstk1003.c
+++ b/arch/avr32/boards/atstk1000/atstk1003.c
@@ -66,6 +66,16 @@ static struct spi_board_info spi1_board_info[] __initdata = { {
 } };
 #endif
 
+#ifndef CONFIG_BOARD_ATSTK100X_SW2_CUSTOM
+static struct mci_platform_data __initdata mci0_data = {
+	.slot[0] = {
+		.bus_width	= 4,
+		.detect_pin	= -ENODEV,
+		.wp_pin		= -ENODEV,
+	},
+};
+#endif
+
 #ifdef CONFIG_BOARD_ATSTK1000_EXTDAC
 static void __init atstk1003_setup_extdac(void)
 {
@@ -154,7 +164,7 @@ static int __init atstk1003_init(void)
 	at32_add_device_spi(1, spi1_board_info, ARRAY_SIZE(spi1_board_info));
 #endif
 #ifndef CONFIG_BOARD_ATSTK100X_SW2_CUSTOM
-	at32_add_device_mci(0, NULL);
+	at32_add_device_mci(0, &mci0_data);
 #endif
 	at32_add_device_usba(0, NULL);
 #ifndef CONFIG_BOARD_ATSTK100X_SW3_CUSTOM
diff --git a/arch/avr32/boards/atstk1000/atstk1004.c b/arch/avr32/boards/atstk1000/atstk1004.c
index 50a5273e5916..d6a2d02f0329 100644
--- a/arch/avr32/boards/atstk1000/atstk1004.c
+++ b/arch/avr32/boards/atstk1000/atstk1004.c
@@ -71,6 +71,16 @@ static struct spi_board_info spi1_board_info[] __initdata = { {
 } };
 #endif
 
+#ifndef CONFIG_BOARD_ATSTK100X_SW2_CUSTOM
+static struct mci_platform_data __initdata mci0_data = {
+	.slot[0] = {
+		.bus_width	= 4,
+		.detect_pin	= -ENODEV,
+		.wp_pin		= -ENODEV,
+	},
+};
+#endif
+
 #ifdef CONFIG_BOARD_ATSTK1000_EXTDAC
 static void __init atstk1004_setup_extdac(void)
 {
@@ -137,7 +147,7 @@ static int __init atstk1004_init(void)
 	at32_add_device_spi(1, spi1_board_info, ARRAY_SIZE(spi1_board_info));
 #endif
 #ifndef CONFIG_BOARD_ATSTK100X_SW2_CUSTOM
-	at32_add_device_mci(0, NULL);
+	at32_add_device_mci(0, &mci0_data);
 #endif
 	at32_add_device_lcdc(0, &atstk1000_lcdc_data,
 			     fbmem_start, fbmem_size, 0);
diff --git a/arch/avr32/include/asm/atmel-mci.h b/arch/avr32/include/asm/atmel-mci.h
index c2ea6e1c9aa1..d38c64ca41e8 100644
--- a/arch/avr32/include/asm/atmel-mci.h
+++ b/arch/avr32/include/asm/atmel-mci.h
@@ -1,9 +1,29 @@
 #ifndef __ASM_AVR32_ATMEL_MCI_H
 #define __ASM_AVR32_ATMEL_MCI_H
 
-struct mci_platform_data {
+/**
+ * struct mci_slot_pdata - board-specific per-slot configuration
+ * @bus_width: Number of data lines wired up the slot
+ * @detect_pin: GPIO pin wired to the card detect switch
+ * @wp_pin: GPIO pin wired to the write protect sensor
+ *
+ * If a given slot is not present on the board, @bus_width should be
+ * set to 0. The other fields are ignored in this case.
+ *
+ * Any pins that aren't available should be set to a negative value.
+ */
+struct mci_slot_pdata {
+	unsigned int		bus_width;
 	int			detect_pin;
 	int			wp_pin;
 };
 
+/**
+ * struct mci_platform_data - board-specific MMC/SDcard configuration
+ * @slot: Per-slot configuration data.
+ */
+struct mci_platform_data {
+	struct mci_slot_pdata	slot[2];
+};
+
 #endif /* __ASM_AVR32_ATMEL_MCI_H */
diff --git a/arch/avr32/mach-at32ap/at32ap700x.c b/arch/avr32/mach-at32ap/at32ap700x.c
index e01dbe4ebb40..9967d5a3b6eb 100644
--- a/arch/avr32/mach-at32ap/at32ap700x.c
+++ b/arch/avr32/mach-at32ap/at32ap700x.c
@@ -1272,10 +1272,13 @@ static struct clk atmel_mci0_pclk = {
 struct platform_device *__init
 at32_add_device_mci(unsigned int id, struct mci_platform_data *data)
 {
-	struct mci_platform_data	_data;
 	struct platform_device		*pdev;
 
-	if (id != 0)
+	if (id != 0 || !data)
+		return NULL;
+
+	/* Must have at least one usable slot */
+	if (!data->slot[0].bus_width && !data->slot[1].bus_width)
 		return NULL;
 
 	pdev = platform_device_alloc("atmel_mci", id);
@@ -1286,28 +1289,61 @@ at32_add_device_mci(unsigned int id, struct mci_platform_data *data)
 				ARRAY_SIZE(atmel_mci0_resource)))
 		goto fail;
 
-	if (!data) {
-		data = &_data;
-		memset(data, -1, sizeof(struct mci_platform_data));
-		data->detect_pin = GPIO_PIN_NONE;
-		data->wp_pin = GPIO_PIN_NONE;
-	}
 
 	if (platform_device_add_data(pdev, data,
 				sizeof(struct mci_platform_data)))
 		goto fail;
 
-	select_peripheral(PA(10), PERIPH_A, 0);	/* CLK	 */
-	select_peripheral(PA(11), PERIPH_A, 0);	/* CMD	 */
-	select_peripheral(PA(12), PERIPH_A, 0);	/* DATA0 */
-	select_peripheral(PA(13), PERIPH_A, 0);	/* DATA1 */
-	select_peripheral(PA(14), PERIPH_A, 0);	/* DATA2 */
-	select_peripheral(PA(15), PERIPH_A, 0);	/* DATA3 */
+	/* CLK line is common to both slots */
+	select_peripheral(PA(10), PERIPH_A, 0);
 
-	if (gpio_is_valid(data->detect_pin))
-		at32_select_gpio(data->detect_pin, 0);
-	if (gpio_is_valid(data->wp_pin))
-		at32_select_gpio(data->wp_pin, 0);
+	switch (data->slot[0].bus_width) {
+	case 4:
+		select_peripheral(PA(13), PERIPH_A, 0);	/* DATA1 */
+		select_peripheral(PA(14), PERIPH_A, 0);	/* DATA2 */
+		select_peripheral(PA(15), PERIPH_A, 0);	/* DATA3 */
+		/* fall through */
+	case 1:
+		select_peripheral(PA(11), PERIPH_A, 0);	/* CMD	 */
+		select_peripheral(PA(12), PERIPH_A, 0);	/* DATA0 */
+
+		if (gpio_is_valid(data->slot[0].detect_pin))
+			at32_select_gpio(data->slot[0].detect_pin, 0);
+		if (gpio_is_valid(data->slot[0].wp_pin))
+			at32_select_gpio(data->slot[0].wp_pin, 0);
+		break;
+	case 0:
+		/* Slot is unused */
+		break;
+	default:
+		goto fail;
+	}
+
+	switch (data->slot[1].bus_width) {
+	case 4:
+		select_peripheral(PB(8),  PERIPH_B, 0);	/* DATA1 */
+		select_peripheral(PB(9),  PERIPH_B, 0);	/* DATA2 */
+		select_peripheral(PB(10), PERIPH_B, 0);	/* DATA3 */
+		/* fall through */
+	case 1:
+		select_peripheral(PB(6),  PERIPH_B, 0); /* CMD	 */
+		select_peripheral(PB(7),  PERIPH_B, 0); /* DATA0 */
+
+		if (gpio_is_valid(data->slot[1].detect_pin))
+			at32_select_gpio(data->slot[1].detect_pin, 0);
+		if (gpio_is_valid(data->slot[1].wp_pin))
+			at32_select_gpio(data->slot[1].wp_pin, 0);
+		break;
+	case 0:
+		/* Slot is unused */
+		break;
+	default:
+		if (!data->slot[0].bus_width)
+			goto fail;
+
+		data->slot[1].bus_width = 0;
+		break;
+	}
 
 	atmel_mci0_pclk.dev = &pdev->dev;
 
diff --git a/drivers/mmc/host/atmel-mci-regs.h b/drivers/mmc/host/atmel-mci-regs.h
index 26bd80e65031..b58364ed6bba 100644
--- a/drivers/mmc/host/atmel-mci-regs.h
+++ b/drivers/mmc/host/atmel-mci-regs.h
@@ -25,8 +25,10 @@
 #define MCI_SDCR		0x000c	/* SD Card / SDIO */
 # define MCI_SDCSEL_SLOT_A	(  0 <<  0)	/* Select SD slot A */
 # define MCI_SDCSEL_SLOT_B	(  1 <<  0)	/* Select SD slot A */
-# define MCI_SDCBUS_1BIT	(  0 <<  7)	/* 1-bit data bus */
-# define MCI_SDCBUS_4BIT	(  1 <<  7)	/* 4-bit data bus */
+# define MCI_SDCSEL_MASK	(  3 <<  0)
+# define MCI_SDCBUS_1BIT	(  0 <<  6)	/* 1-bit data bus */
+# define MCI_SDCBUS_4BIT	(  2 <<  6)	/* 4-bit data bus */
+# define MCI_SDCBUS_MASK	(  3 <<  6)
 #define MCI_ARGR		0x0010	/* Command Argument */
 #define MCI_CMDR		0x0014	/* Command */
 # define MCI_CMDR_CMDNB(x)	((x) <<  0)	/* Command Opcode */
diff --git a/drivers/mmc/host/atmel-mci.c b/drivers/mmc/host/atmel-mci.c
index 14ab28da7fa8..8170905a0401 100644
--- a/drivers/mmc/host/atmel-mci.c
+++ b/drivers/mmc/host/atmel-mci.c
@@ -508,9 +508,10 @@ static void atmci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 {
 	struct atmel_mci	*host = mmc_priv(mmc);
 
+	host->sdc_reg &= ~MCI_SDCBUS_MASK;
 	switch (ios->bus_width) {
 	case MMC_BUS_WIDTH_1:
-		host->sdc_reg = 0;
+		host->sdc_reg |= MCI_SDCBUS_1BIT;
 		break;
 	case MMC_BUS_WIDTH_4:
 		host->sdc_reg = MCI_SDCBUS_4BIT;
@@ -1014,9 +1015,11 @@ static irqreturn_t atmci_detect_interrupt(int irq, void *dev_id)
 static int __init atmci_probe(struct platform_device *pdev)
 {
 	struct mci_platform_data	*pdata;
+	struct mci_slot_pdata		*slot;
 	struct atmel_mci *host;
 	struct mmc_host *mmc;
 	struct resource *regs;
+	u32 sdc_reg;
 	int irq;
 	int ret;
 
@@ -1030,6 +1033,17 @@ static int __init atmci_probe(struct platform_device *pdev)
 	if (irq < 0)
 		return irq;
 
+	/* TODO: Allow using several slots at once */
+	if (pdata->slot[0].bus_width) {
+		sdc_reg = MCI_SDCSEL_SLOT_A;
+		slot = &pdata->slot[0];
+	} else if (pdata->slot[1].bus_width) {
+		sdc_reg = MCI_SDCSEL_SLOT_B;
+		slot = &pdata->slot[1];
+	} else {
+		return -EINVAL;
+	}
+
 	mmc = mmc_alloc_host(sizeof(struct atmel_mci), &pdev->dev);
 	if (!mmc)
 		return -ENOMEM;
@@ -1037,8 +1051,9 @@ static int __init atmci_probe(struct platform_device *pdev)
 	host = mmc_priv(mmc);
 	host->pdev = pdev;
 	host->mmc = mmc;
-	host->detect_pin = pdata->detect_pin;
-	host->wp_pin = pdata->wp_pin;
+	host->detect_pin = slot->detect_pin;
+	host->wp_pin = slot->wp_pin;
+	host->sdc_reg = sdc_reg;
 
 	host->mck = clk_get(&pdev->dev, "mci_clk");
 	if (IS_ERR(host->mck)) {
@@ -1062,7 +1077,8 @@ static int __init atmci_probe(struct platform_device *pdev)
 	mmc->f_min = (host->bus_hz + 511) / 512;
 	mmc->f_max = host->bus_hz / 2;
 	mmc->ocr_avail	= MMC_VDD_32_33 | MMC_VDD_33_34;
-	mmc->caps |= MMC_CAP_4_BIT_DATA;
+	if (slot->bus_width >= 4)
+		mmc->caps |= MMC_CAP_4_BIT_DATA;
 
 	mmc->max_hw_segs = 64;
 	mmc->max_phys_segs = 64;