diff --git a/drivers/mfd/asic3.c b/drivers/mfd/asic3.c
index f2fb233b0ff3..3b870e7fb3e1 100644
--- a/drivers/mfd/asic3.c
+++ b/drivers/mfd/asic3.c
@@ -313,6 +313,7 @@ static int __init asic3_irq_probe(struct platform_device *pdev)
 	struct asic3 *asic = platform_get_drvdata(pdev);
 	unsigned long clksel = 0;
 	unsigned int irq, irq_base;
+	int map_size;
 
 	asic->irq_nr = platform_get_irq(pdev, 0);
 	if (asic->irq_nr < 0)
@@ -551,8 +552,8 @@ static int __init asic3_probe(struct platform_device *pdev)
 		goto out_free;
 	}
 
-
-	asic->mapping = ioremap(mem->start, PAGE_SIZE);
+	map_size = mem->end - mem->start + 1;
+	asic->mapping = ioremap(mem->start, map_size);
 	if (!asic->mapping) {
 		ret = -ENOMEM;
 		dev_err(asic->dev, "Couldn't ioremap\n");
@@ -561,10 +562,8 @@ static int __init asic3_probe(struct platform_device *pdev)
 
 	asic->irq_base = pdata->irq_base;
 
-	if (pdata && pdata->bus_shift)
-		asic->bus_shift = 2 - pdata->bus_shift;
-	else
-		asic->bus_shift = 0;
+	/* calculate bus shift from mem resource */
+	asic->bus_shift = 2 - (map_size >> 12);
 
 	clksel = 0;
 	asic3_write_register(asic, ASIC3_OFFSET(CLOCK, SEL), clksel);
diff --git a/include/linux/mfd/asic3.h b/include/linux/mfd/asic3.h
index 8f8c46c41f44..322cd6deb9f0 100644
--- a/include/linux/mfd/asic3.h
+++ b/include/linux/mfd/asic3.h
@@ -20,8 +20,6 @@ struct asic3_platform_data {
 	u16 *gpio_config;
 	unsigned int gpio_config_num;
 
-	unsigned int bus_shift;
-
 	unsigned int irq_base;
 
 	unsigned int gpio_base;
@@ -498,6 +496,7 @@ struct asic3_platform_data {
 #define ASIC3_SDIO_CTRL_LEDCtrl              0x7C
 #define ASIC3_SDIO_CTRL_SoftwareReset        0x1C0
 
-#define ASIC3_MAP_SIZE	     		     0x2000
+#define ASIC3_MAP_SIZE_32BIT	0x2000
+#define ASIC3_MAP_SIZE_16BIT	0x1000
 
 #endif /* __ASIC3_H__ */