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

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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: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Guenter Roeck 2021-11-05 16:04:52 -07:00
parent b2644494a4
commit 8f19501d87
1 changed files with 23 additions and 18 deletions
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41
drivers/hwmon/lm90.c
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@ -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;