w1: IAD Register is yet readable trough iad sys file. Fix snprintf (%u for unsigned, count for max size).

IAD Register is yet readable trough the "iad" sys file.

A write to the "iad" sys file enables or disables the current
measurement, but it was not possible to get the measured value by
reading it.
Fix: %u in snprintf for unsigned values (vdd and vad)
Fix: Avoid possibles overflows (Usage of the 'count' variables)

Signed-off-by: Julien Folly <julien.folly@gmail.com>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/w1/slaves/w1_ds2438.c b/drivers/w1/slaves/w1_ds2438.c
index bf641a1..7c4e33d 100644
--- a/drivers/w1/slaves/w1_ds2438.c
+++ b/drivers/w1/slaves/w1_ds2438.c
@@ -186,8 +186,8 @@
 	return -1;
 }
 
-static uint16_t w1_ds2438_get_voltage(struct w1_slave *sl,
-				      int adc_input, uint16_t *voltage)
+static int w1_ds2438_get_voltage(struct w1_slave *sl,
+				 int adc_input, uint16_t *voltage)
 {
 	unsigned int retries = W1_DS2438_RETRIES;
 	u8 w1_buf[DS2438_PAGE_SIZE + 1 /*for CRC*/];
@@ -235,6 +235,25 @@
 	return ret;
 }
 
+static int w1_ds2438_get_current(struct w1_slave *sl, int16_t *voltage)
+{
+	u8 w1_buf[DS2438_PAGE_SIZE + 1 /*for CRC*/];
+	int ret;
+
+	mutex_lock(&sl->master->bus_mutex);
+
+	if (w1_ds2438_get_page(sl, 0, w1_buf) == 0) {
+		/* The voltage measured across current sense resistor RSENS. */
+		*voltage = (((int16_t) w1_buf[DS2438_CURRENT_MSB]) << 8) | ((int16_t) w1_buf[DS2438_CURRENT_LSB]);
+		ret = 0;
+	} else
+		ret = -1;
+
+	mutex_unlock(&sl->master->bus_mutex);
+
+	return ret;
+}
+
 static ssize_t iad_write(struct file *filp, struct kobject *kobj,
 			 struct bin_attribute *bin_attr, char *buf,
 			 loff_t off, size_t count)
@@ -257,6 +276,27 @@
 	return ret;
 }
 
+static ssize_t iad_read(struct file *filp, struct kobject *kobj,
+			struct bin_attribute *bin_attr, char *buf,
+			loff_t off, size_t count)
+{
+	struct w1_slave *sl = kobj_to_w1_slave(kobj);
+	int ret;
+	int16_t voltage;
+
+	if (off != 0)
+		return 0;
+	if (!buf)
+		return -EINVAL;
+
+	if (w1_ds2438_get_current(sl, &voltage) == 0) {
+		ret = snprintf(buf, count, "%i\n", voltage);
+	} else
+		ret = -EIO;
+
+	return ret;
+}
+
 static ssize_t page0_read(struct file *filp, struct kobject *kobj,
 			  struct bin_attribute *bin_attr, char *buf,
 			  loff_t off, size_t count)
@@ -272,9 +312,13 @@
 
 	mutex_lock(&sl->master->bus_mutex);
 
+	/* Read no more than page0 size */
+	if (count > DS2438_PAGE_SIZE)
+		count = DS2438_PAGE_SIZE;
+
 	if (w1_ds2438_get_page(sl, 0, w1_buf) == 0) {
-		memcpy(buf, &w1_buf, DS2438_PAGE_SIZE);
-		ret = DS2438_PAGE_SIZE;
+		memcpy(buf, &w1_buf, count);
+		ret = count;
 	} else
 		ret = -EIO;
 
@@ -289,7 +333,6 @@
 {
 	struct w1_slave *sl = kobj_to_w1_slave(kobj);
 	int ret;
-	ssize_t c = PAGE_SIZE;
 	int16_t temp;
 
 	if (off != 0)
@@ -298,8 +341,7 @@
 		return -EINVAL;
 
 	if (w1_ds2438_get_temperature(sl, &temp) == 0) {
-		c -= snprintf(buf + PAGE_SIZE - c, c, "%d\n", temp);
-		ret = PAGE_SIZE - c;
+		ret = snprintf(buf, count, "%i\n", temp);
 	} else
 		ret = -EIO;
 
@@ -312,7 +354,6 @@
 {
 	struct w1_slave *sl = kobj_to_w1_slave(kobj);
 	int ret;
-	ssize_t c = PAGE_SIZE;
 	uint16_t voltage;
 
 	if (off != 0)
@@ -321,8 +362,7 @@
 		return -EINVAL;
 
 	if (w1_ds2438_get_voltage(sl, DS2438_ADC_INPUT_VAD, &voltage) == 0) {
-		c -= snprintf(buf + PAGE_SIZE - c, c, "%d\n", voltage);
-		ret = PAGE_SIZE - c;
+		ret = snprintf(buf, count, "%u\n", voltage);
 	} else
 		ret = -EIO;
 
@@ -335,7 +375,6 @@
 {
 	struct w1_slave *sl = kobj_to_w1_slave(kobj);
 	int ret;
-	ssize_t c = PAGE_SIZE;
 	uint16_t voltage;
 
 	if (off != 0)
@@ -344,15 +383,14 @@
 		return -EINVAL;
 
 	if (w1_ds2438_get_voltage(sl, DS2438_ADC_INPUT_VDD, &voltage) == 0) {
-		c -= snprintf(buf + PAGE_SIZE - c, c, "%d\n", voltage);
-		ret = PAGE_SIZE - c;
+		ret = snprintf(buf, count, "%u\n", voltage);
 	} else
 		ret = -EIO;
 
 	return ret;
 }
 
-static BIN_ATTR(iad, S_IRUGO | S_IWUSR | S_IWGRP, NULL, iad_write, 1);
+static BIN_ATTR(iad, S_IRUGO | S_IWUSR | S_IWGRP, iad_read, iad_write, 0);
 static BIN_ATTR_RO(page0, DS2438_PAGE_SIZE);
 static BIN_ATTR_RO(temperature, 0/* real length varies */);
 static BIN_ATTR_RO(vad, 0/* real length varies */);