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SubjectRe: [PATCH] lm75: add lm75b detection
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On 10/26/19 1:10 AM, Rain Wang wrote:
> The National Semiconductor LM75B is very similar as the
> LM75A, but it has no ID byte register 7, and unused registers
> return 0xff rather than the last read value like LM75A.
>
> Signed-off-by: Rain Wang <rain_wang@jabil.com>

I am quite hesitant to touch the detect function for this chip.
Each addition increases the risk for false positives. What is the
use case ?

Thanks,
Guenter

> ---
> drivers/hwmon/lm75.c | 17 +++++++++++++++--
> 1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hwmon/lm75.c b/drivers/hwmon/lm75.c
> index 5e6392294c03..a718f9eb4d72 100644
> --- a/drivers/hwmon/lm75.c
> +++ b/drivers/hwmon/lm75.c
> @@ -760,6 +760,7 @@ static int lm75_detect(struct i2c_client *new_client,
> int i;
> int conf, hyst, os;
> bool is_lm75a = 0;
> + bool is_lm75b = 0;
>
> if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
> I2C_FUNC_SMBUS_WORD_DATA))
> @@ -780,8 +781,12 @@ static int lm75_detect(struct i2c_client *new_client,
> * register 7, and unused registers return 0xff rather than the
> * last read value.
> *
> + * The National Semiconductor LM75B is very similar as the
> + * LM75A, but it has no ID byte register 7, and unused registers
> + * return 0xff rather than the last read value like LM75A.
> + *
> * Note that this function only detects the original National
> - * Semiconductor LM75 and the LM75A. Clones from other vendors
> + * Semiconductor LM75 and the LM75A/B. Clones from other vendors
> * aren't detected, on purpose, because they are typically never
> * found on PC hardware. They are found on embedded designs where
> * they can be instantiated explicitly so detection is not needed.
> @@ -806,6 +811,13 @@ static int lm75_detect(struct i2c_client *new_client,
> is_lm75a = 1;
> hyst = i2c_smbus_read_byte_data(new_client, 2);
> os = i2c_smbus_read_byte_data(new_client, 3);
> + } else if (i2c_smbus_read_byte_data(new_client, 4) == 0xff
> + && i2c_smbus_read_byte_data(new_client, 5) == 0xff
> + && i2c_smbus_read_byte_data(new_client, 6) == 0xff) {
> + /* LM75B detection */
> + is_lm75b = 1;
> + hyst = i2c_smbus_read_byte_data(new_client, 2);
> + os = i2c_smbus_read_byte_data(new_client, 3);
> } else { /* Traditional style LM75 detection */
> /* Unused addresses */
> hyst = i2c_smbus_read_byte_data(new_client, 2);
> @@ -839,7 +851,8 @@ static int lm75_detect(struct i2c_client *new_client,
> return -ENODEV;
> }
>
> - strlcpy(info->type, is_lm75a ? "lm75a" : "lm75", I2C_NAME_SIZE);
> + strlcpy(info->type, is_lm75a ?
> + "lm75a" : (is_lm75b ? "lm75b" : "lm75"), I2C_NAME_SIZE);
>
> return 0;
> }
>

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