w1: ds1wm: fix register offset (bus shift) calculation

Replace incorrect register offsett calculation by
direct configuration of bus_shift in mfd-cell.

Indirect definition of address-shift by resource size
was unobvious and was wrong (should have used a binary log).
Signed-off-by: Johannes Poehlmann <johannes.poehlmann@izt-labs.de>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/w1/masters/ds1wm.c

@@ -95,7 +95,7 @@ static struct {
 
 struct ds1wm_data {
 	void     __iomem *map;
-	int      bus_shift; /* # of shifts to calc register offsets */
+	unsigned int      bus_shift; /* # of shifts to calc register offsets */
 	struct platform_device *pdev;
 	const struct mfd_cell   *cell;
 	int      irq;
@@ -473,9 +473,6 @@ static int ds1wm_probe(struct platform_device *pdev)
 	if (!ds1wm_data->map)
 		return -ENOMEM;
 
-	/* calculate bus shift from mem resource */
-	ds1wm_data->bus_shift = resource_size(res) >> 3;
-
 	ds1wm_data->pdev = pdev;
 	ds1wm_data->cell = mfd_get_cell(pdev);
 	if (!ds1wm_data->cell)
@@ -484,6 +481,24 @@ static int ds1wm_probe(struct platform_device *pdev)
 	if (!plat)
 		return -ENODEV;
 
+	/* how many bits to shift register number to get register offset */
+	if (plat->bus_shift > 2) {
+		dev_err(&ds1wm_data->pdev->dev,
+			"illegal bus shift %d, not written",
+			ds1wm_data->bus_shift);
+		return -EINVAL;
+	}
+
+	ds1wm_data->bus_shift = plat->bus_shift;
+	/* make sure resource has space for 8 registers */
+	if ((8 << ds1wm_data->bus_shift) > resource_size(res)) {
+		dev_err(&ds1wm_data->pdev->dev,
+			"memory resource size %d to small, should be %d\n",
+			(int)resource_size(res),
+			8 << ds1wm_data->bus_shift);
+		return -EINVAL;
+	}
+
 	res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
 	if (!res)
 		return -ENXIO;

include/linux/mfd/ds1wm.h

-/* MFD cell driver data for the DS1WM driver */
+/* MFD cell driver data for the DS1WM driver
+ *
+ * to be defined in the MFD device that is
+ * using this driver for one of his sub devices
+ */
 
 struct ds1wm_driver_data {
 	int active_high;
 	int clock_rate;
-	/* in milliseconds, the amount of time to */
-	/* sleep following a reset pulse. Zero    */
-	/* should work if your bus devices recover*/
-	/* time respects the 1-wire spec since the*/
-	/* ds1wm implements the precise timings of*/
-	/* a reset pulse/presence detect sequence.*/
+	/* in milliseconds, the amount of time to
+	 * sleep following a reset pulse. Zero
+	 * should work if your bus devices recover
+	 * time respects the 1-wire spec since the
+	 * ds1wm implements the precise timings of
+	 * a reset pulse/presence detect sequence.
+	 */
 	unsigned int reset_recover_delay;
+
+	/* left shift of register number to get register address offsett.
+	 * Only 0,1,2 allowed for 8,16 or 32 bit bus width respectively
+	 */
+	unsigned int bus_shift;
 };