[PATCH 3/3] w1: ds2438: adding support for accessing page1 registers

[Luiz Sampaio <sampaio.ime@gmail.com>]

The ds2438 has a register in page1 called offset, which dictates
how the current measurement is done. If the offset register is not
calibrated well, pulling zero current from a battery shows a non-zero
current measurement.
Gives write access to the offset register. This way, a user following
the calibration steps explained in the datasheet can use this driver
to fully calibrate de current measurements.

Signed-off-by: Luiz Sampaio <sampaio.ime@gmail.com>
---
 drivers/w1/slaves/w1_ds2438.c | 94 ++++++++++++++++++++++++++++++++++-
 1 file changed, 92 insertions(+), 2 deletions(-)

diff --git a/drivers/w1/slaves/w1_ds2438.c b/drivers/w1/slaves/w1_ds2438.c
index 08f4b451c349..5d58986bb1a9 100644
--- a/drivers/w1/slaves/w1_ds2438.c
+++ b/drivers/w1/slaves/w1_ds2438.c
@@ -49,6 +49,15 @@
 #define DS2438_CURRENT_MSB		0x06
 #define DS2438_THRESHOLD		0x07
 
+/* Page #1 definitions */
+#define DS2438_ETM_0			0x00
+#define DS2438_ETM_1			0x01
+#define DS2438_ETM_2			0x02
+#define DS2438_ETM_3			0x03
+#define DS2438_ICA			0x04
+#define DS2438_OFFSET_LSB		0x05
+#define DS2438_OFFSET_MSB		0x06
+
 static int w1_ds2438_get_page(struct w1_slave *sl, int pageno, u8 *buf)
 {
 	unsigned int retries = W1_DS2438_RETRIES;
@@ -62,13 +71,13 @@ static int w1_ds2438_get_page(struct w1_slave *sl, int pageno, u8 *buf)
 		if (w1_reset_select_slave(sl))
 			continue;
 		w1_buf[0] = W1_DS2438_RECALL_MEMORY;
-		w1_buf[1] = pageno;
+		w1_buf[1] = (u8)pageno;
 		w1_write_block(sl->master, w1_buf, 2);
 
 		if (w1_reset_select_slave(sl))
 			continue;
 		w1_buf[0] = W1_DS2438_READ_SCRATCH;
-		w1_buf[1] = pageno;
+		w1_buf[1] = (u8)pageno;
 		w1_write_block(sl->master, w1_buf, 2);
 
 		count = w1_read_block(sl->master, buf, DS2438_PAGE_SIZE + 1);
@@ -182,6 +191,34 @@ static int w1_ds2438_change_config_bit(struct w1_slave *sl, u8 mask, u8 value)
 	return -1;
 }
 
+static int w1_ds2438_change_offset_register(struct w1_slave *sl, u8 *value)
+{
+	unsigned int retries = W1_DS2438_RETRIES;
+	u8 w1_buf[9];
+	u8 w1_page1_buf[DS2438_PAGE_SIZE + 1 /*for CRC*/];
+
+	if (w1_ds2438_get_page(sl, 1, w1_page1_buf) == 0) {
+		memcpy(&w1_buf[2], w1_page1_buf, DS2438_PAGE_SIZE - 1); /* last register is reserved */
+		w1_buf[7] = value[0]; /* change only offset register */
+		w1_buf[8] = value[1];
+		while (retries--) {
+			if (w1_reset_select_slave(sl))
+				continue;
+			w1_buf[0] = W1_DS2438_WRITE_SCRATCH;
+			w1_buf[1] = 0x01; /* write to page 1 */
+			w1_write_block(sl->master, w1_buf, 9);
+
+			if (w1_reset_select_slave(sl))
+				continue;
+			w1_buf[0] = W1_DS2438_COPY_SCRATCH;
+			w1_buf[1] = 0x01;
+			w1_write_block(sl->master, w1_buf, 2);
+				return 0;
+		}
+	}
+	return -1;
+}
+
 static int w1_ds2438_get_voltage(struct w1_slave *sl,
 				 int adc_input, uint16_t *voltage)
 {
@@ -323,6 +360,55 @@ static ssize_t page0_read(struct file *filp, struct kobject *kobj,
 	return ret;
 }
 
+static ssize_t page1_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;
+	u8 w1_buf[DS2438_PAGE_SIZE + 1 /*for CRC*/];
+
+	if (off != 0)
+		return 0;
+	if (!buf)
+		return -EINVAL;
+
+	mutex_lock(&sl->master->bus_mutex);
+
+	/* Read no more than page1 size */
+	if (count > DS2438_PAGE_SIZE)
+		count = DS2438_PAGE_SIZE;
+
+	if (w1_ds2438_get_page(sl, 1, w1_buf) == 0) {
+		memcpy(buf, &w1_buf, count);
+		ret = count;
+	} else
+		ret = -EIO;
+
+	mutex_unlock(&sl->master->bus_mutex);
+
+	return ret;
+}
+
+static ssize_t offset_write(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;
+
+	mutex_lock(&sl->master->bus_mutex);
+
+	if (w1_ds2438_change_offset_register(sl, buf) == 0)
+		ret = count;
+	else
+		ret = -EIO;
+
+	mutex_unlock(&sl->master->bus_mutex);
+
+	return ret;
+}
+
 static ssize_t temperature_read(struct file *filp, struct kobject *kobj,
 				struct bin_attribute *bin_attr, char *buf,
 				loff_t off, size_t count)
@@ -388,6 +474,8 @@ static ssize_t vdd_read(struct file *filp, struct kobject *kobj,
 
 static BIN_ATTR(iad, 0664, iad_read, iad_write, 0);
 static BIN_ATTR_RO(page0, DS2438_PAGE_SIZE);
+static BIN_ATTR_RO(page1, DS2438_PAGE_SIZE);
+static BIN_ATTR_WO(offset, 2);
 static BIN_ATTR_RO(temperature, 0/* real length varies */);
 static BIN_ATTR_RO(vad, 0/* real length varies */);
 static BIN_ATTR_RO(vdd, 0/* real length varies */);
@@ -395,6 +483,8 @@ static BIN_ATTR_RO(vdd, 0/* real length varies */);
 static struct bin_attribute *w1_ds2438_bin_attrs[] = {
 	&bin_attr_iad,
 	&bin_attr_page0,
+	&bin_attr_page1,
+	&bin_attr_offset,
 	&bin_attr_temperature,
 	&bin_attr_vad,
 	&bin_attr_vdd,
-- 
2.30.1