Commit 8f19501d authored by Guenter Roeck's avatar Guenter Roeck
Browse files

hwmon: (lm90) Only re-read registers if volatile 



When reading 16-bit volatile registers, the code uses a trick to
determine if a temperature is consistent: It reads the high part
of the register twice. If the values are the same, the code assumes
that the reading is consistent. If the value differs, the code
re-reads the second register as well and assumes that it now has
correct values.

This is only necessary for volatile registers. Add a parameter to
lm90_read16() to indicate if the register is volatile to avoid the
extra overhead for non-volatile registers.

Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
parent b2644494

drivers/hwmon/lm90.c

+23 −18
Original line number Diff line number Diff line
@@ -602,29 +602,34 @@ static int lm90_write_reg(struct i2c_client *client, u8 reg, u8 val) 
	return i2c_smbus_write_byte_data(client, lm90_write_reg_addr(reg), val);

}



static int lm90_read16(struct i2c_client *client, u8 regh, u8 regl)

static int lm90_read16(struct i2c_client *client, u8 regh, u8 regl,

		       bool is_volatile)

{

	int oldh, newh, l;



	/*

	 * There is a trick here. We have to read two registers to have the

	 * sensor temperature, but we have to beware a conversion could occur

	 * between the readings. The datasheet says we should either use

	 * the one-shot conversion register, which we don't want to do

	 * (disables hardware monitoring) or monitor the busy bit, which is

	 * impossible (we can't read the values and monitor that bit at the

	 * exact same time). So the solution used here is to read the high

	 * byte once, then the low byte, then the high byte again. If the new

	 * high byte matches the old one, then we have a valid reading. Else

	 * we have to read the low byte again, and now we believe we have a

	 * correct reading.

	 */

	oldh = lm90_read_reg(client, regh);

	if (oldh < 0)

		return oldh;

	l = lm90_read_reg(client, regl);

	if (l < 0)

		return l;



	if (!is_volatile)

		return (oldh << 8) | l;



	/*

	 * For volatile registers we have to use a trick.

	 * We have to read two registers to have the sensor temperature,

	 * but we have to beware a conversion could occur between the

	 * readings. The datasheet says we should either use

	 * the one-shot conversion register, which we don't want to do

	 * (disables hardware monitoring) or monitor the busy bit, which is

	 * impossible (we can't read the values and monitor that bit at the

	 * exact same time). So the solution used here is to read the high

	 * the high byte again. If the new high byte matches the old one,

	 * then we have a valid reading. Otherwise we have to read the low

	 * byte again, and now we believe we have a correct reading.

	 */

	newh = lm90_read_reg(client, regh);

	if (newh < 0)

		return newh;
@@ -766,7 +771,7 @@ static int lm90_update_limits(struct device *dev) 


	if (data->flags & LM90_HAVE_OFFSET) {

		val = lm90_read16(client, LM90_REG_REMOTE_OFFSH,

				  LM90_REG_REMOTE_OFFSL);

				  LM90_REG_REMOTE_OFFSL, false);

		if (val < 0)

			return val;

		data->temp11[REMOTE_OFFSET] = val;
@@ -999,7 +1004,7 @@ static int lm90_update_device(struct device *dev) 


		if (data->reg_local_ext) {

			val = lm90_read16(client, LM90_REG_LOCAL_TEMP,

					  data->reg_local_ext);

					  data->reg_local_ext, true);

			if (val < 0)

				return val;

			data->temp11[LOCAL_TEMP] = val;
@@ -1010,7 +1015,7 @@ static int lm90_update_device(struct device *dev) 
			data->temp11[LOCAL_TEMP] = val << 8;

		}

		val = lm90_read16(client, LM90_REG_REMOTE_TEMPH,

				  LM90_REG_REMOTE_TEMPL);

				  LM90_REG_REMOTE_TEMPL, true);

		if (val < 0)

			return val;

		data->temp11[REMOTE_TEMP] = val;
@@ -1021,7 +1026,7 @@ static int lm90_update_device(struct device *dev) 
				return val;



			val = lm90_read16(client, LM90_REG_REMOTE_TEMPH,

					  LM90_REG_REMOTE_TEMPL);

					  LM90_REG_REMOTE_TEMPL, true);

			if (val < 0) {

				lm90_select_remote_channel(data, 0);

				return val;