Re: [PATCH v1] hwmon: (lm75) Add support for Nuvoton NCT7715

[Sheng-Yuan Huang]

Thank you for the review. I may have misunderstood which conversion
you are referring to, so I would like to clarify both parts.

If this refers to the NCT7715_CONFIG_* masks, they use the logical bit
positions of the 16-bit configuration register defined by the
NCT7715 specification. They are not pre-swapped for the SMBus word
byte order.

If this refers to the I2C accessors, the NCT7715 transfers its 16-bit
configuration register MSB first. The lm75 regmap bus uses
reg_read/reg_write callbacks. In this path, regmap passes the logical
register value to the callbacks, and i2c_smbus_*_word_swapped()
performs the conversion between that value and the SMBus word byte
order.

I verified this on hardware by changing update_interval. i2cget shows
0xe060, 0xa060, 0x6060, and 0x2060 for 125, 250, 1000, and 4000 ms,
respectively. After accounting for the SMBus word byte order, these
are logical values 0x60e0, 0x60a0, 0x6060, and 0x6020. In each case,
only the NCT7715 conversion-rate field, bits [7:6], is changed.

Guenter Roeck <linux@xxxxxxxxxxxx> 於 2026年9月7日週一 下午11:30寫道：
>
> On 9/7/26 01:08, hsyemail2@xxxxxxxxx wrote:
> > From: Sheng-Yuan Huang <syhuang3@xxxxxxxxxxx>
> >
> > The Nuvoton NCT7715 is compatible with the LM75 temperature and
> > limit register layout, but its 16-bit configuration register is
> > transmitted most-significant byte first. Add support for the NCT7715,
> > including byte-swapped SMBus accesses for its configuration register.
> >
> > Handle its conversion-rate field and shutdown bit separately, since
> > their bit positions differ from the standard LM75 layout.
> >
> I don't think so. See below.
>
> > Signed-off-by: Sheng-Yuan Huang <syhuang3@xxxxxxxxxxx>
> > ---
> >   .../devicetree/bindings/hwmon/lm75.yaml       |  1 +
> >   Documentation/hwmon/lm75.rst                  |  6 ++
> >   drivers/hwmon/lm75.c                          | 57 ++++++++++++++++++-
> >   3 files changed, 62 insertions(+), 2 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/hwmon/lm75.yaml b/Documentation/devicetree/bindings/hwmon/lm75.yaml
> > index b48bf3fd721f..832a8c5d83e9 100644
> > --- a/Documentation/devicetree/bindings/hwmon/lm75.yaml
> > +++ b/Documentation/devicetree/bindings/hwmon/lm75.yaml
> > @@ -31,6 +31,7 @@ properties:
> >         - nxp,p3t1750
> >         - nxp,p3t1755
> >         - nxp,pct2075
> > +      - nuvoton,nct7715
> >         - st,stds75
> >         - st,stlm75
> >         - microchip,tcn75
> > diff --git a/Documentation/hwmon/lm75.rst b/Documentation/hwmon/lm75.rst
> > index ca46754e028b..fac0b8f29ddc 100644
> > --- a/Documentation/hwmon/lm75.rst
> > +++ b/Documentation/hwmon/lm75.rst
> > @@ -150,6 +150,12 @@ Supported chips:
> >
> >                  https://ams.com/documents/20143/36005/AS6200_DS000449_4-00.pdf
> >
> > +  * Nuvoton NCT7715
> > +
> > +    Prefix: 'nct7715'
> > +
> > +    Addresses scanned: none
> > +
> >   Author: Frodo Looijaard <frodol@xxxxxx>
> >
> >   Description
> > diff --git a/drivers/hwmon/lm75.c b/drivers/hwmon/lm75.c
> > index 2d2d752aeac9..0b55f6b7c68d 100644
> > --- a/drivers/hwmon/lm75.c
> > +++ b/drivers/hwmon/lm75.c
> > @@ -39,6 +39,7 @@ enum lm75_type {            /* keep sorted in alphabetical order */
> >       max6626,
> >       max31725,
> >       mcp980x,
> > +     nct7715,
> >       p3t1750,
> >       p3t1755,
> >       pct2075,
> > @@ -107,6 +108,15 @@ static const unsigned short normal_i2c[] = { 0x48, 0x49, 0x4a, 0x4b, 0x4c,
> >   #define LM75_REG_MAX                0x03
> >   #define PCT2075_REG_IDLE    0x04
> >
> > +#define NCT7715_CONFIG_RESOLUTION_12_BIT     GENMASK(14, 13)
> > +#define NCT7715_CONFIG_SHUTDOWN                      BIT(8)
> > +#define NCT7715_CONFIG_CONVERSION_RATE_MASK  GENMASK(7, 6)
> > +#define NCT7715_CONFIG_EXTENDED_MODE         BIT(4)
> > +#define NCT7715_CONFIG_RATE_0_25HZ           0
> > +#define NCT7715_CONFIG_RATE_1HZ                      BIT(6)
> > +#define NCT7715_CONFIG_RATE_4HZ                      BIT(7)
> > +#define NCT7715_CONFIG_RATE_8HZ                      GENMASK(7, 6)
> > +
> >   struct lm75_data {
> >       const char *label;
> >       struct regmap                   *regmap;
> > @@ -122,6 +132,10 @@ struct lm75_data {
> >   /*-----------------------------------------------------------------------*/
> >
> >   static const u8 lm75_sample_set_masks[] = { 0 << 5, 1 << 5, 2 << 5, 3 << 5 };
> > +static const u16 nct7715_sample_set_masks[] = {
> > +     NCT7715_CONFIG_RATE_8HZ, NCT7715_CONFIG_RATE_4HZ,
> > +     NCT7715_CONFIG_RATE_1HZ, NCT7715_CONFIG_RATE_0_25HZ
> > +};
> >
> >   #define LM75_ALERT_POLARITY_HIGH_8_BIT      (BIT(2))
> >   #define LM75_ALERT_POLARITY_HIGH_16_BIT     (BIT(2) << 8)
> > @@ -259,6 +273,15 @@ static const struct lm75_params device_params[] = {
> >               .sample_times = (unsigned int []){ 30, 60, 120, 240 },
> >               .resolutions = (u8 []) {9, 10, 11, 12 },
> >       },
> > +     [nct7715] = {
> > +             .config_reg_16bits = true,
> > +             .set_mask = NCT7715_CONFIG_RESOLUTION_12_BIT,
> > +             .clr_mask = NCT7715_CONFIG_EXTENDED_MODE,
> > +             .default_resolution = 12,
> > +             .default_sample_time = 250,
> > +             .num_sample_times = 4,
> > +             .sample_times = (unsigned int []){ 125, 250, 1000, 4000 },
> > +     },
> >       [tmp100] = {
> >               .set_mask = 3 << 5,     /* 12-bit mode */
> >               .clr_mask = 1 << 7,     /* not one-shot mode */
> > @@ -354,6 +377,11 @@ static inline long lm75_reg_to_mc(s16 temp, u8 resolution)
> >   static inline int lm75_write_config(struct lm75_data *data, u16 set_mask,
> >                                   u16 clr_mask)
> >   {
> > +     if (data->kind == nct7715)
> > +             return regmap_update_bits(data->regmap, LM75_REG_CONF,
> > +                                       clr_mask | set_mask | NCT7715_CONFIG_SHUTDOWN,
> > +                                       set_mask);
> > +
> >       return regmap_update_bits(data->regmap, LM75_REG_CONF,
> >                                 clr_mask | set_mask | LM75_SHUTDOWN, set_mask);
> >   }
> > @@ -486,6 +514,13 @@ static int lm75_update_interval(struct device *dev, long val)
> >               if (data->params->resolutions)
> >                       data->resolution = data->params->resolutions[index];
> >               break;
> > +     case nct7715:
> > +             err = lm75_write_config(data, nct7715_sample_set_masks[index],
> > +                                     NCT7715_CONFIG_CONVERSION_RATE_MASK);
> > +             if (err)
> > +                     return err;
> > +             data->sample_time = data->params->sample_times[index];
> > +             break;
> >       case tmp112:
> >       case as6200:
> >               err = regmap_update_bits(data->regmap, LM75_REG_CONF,
> > @@ -609,6 +644,8 @@ static int lm75_i2c_reg_read(void *context, unsigned int reg, unsigned int *val)
> >       if (reg == LM75_REG_CONF) {
> >               if (!data->params->config_reg_16bits)
> >                       ret = i2c_smbus_read_byte_data(client, LM75_REG_CONF);
> > +             else if (data->kind == nct7715)
> > +                     ret = i2c_smbus_read_word_swapped(client, LM75_REG_CONF);
> >               else
> >                       ret = i2c_smbus_read_word_data(client, LM75_REG_CONF);
> >       } else {
> > @@ -628,8 +665,11 @@ static int lm75_i2c_reg_write(void *context, unsigned int reg, unsigned int val)
> >       if (reg == PCT2075_REG_IDLE ||
> >           (reg == LM75_REG_CONF && !data->params->config_reg_16bits))
> >               return i2c_smbus_write_byte_data(client, reg, val);
> > -     else if (reg == LM75_REG_CONF)
> > +     else if (reg == LM75_REG_CONF) {
> > +             if (data->kind == nct7715)
> > +                     return i2c_smbus_write_word_swapped(client, reg, val);
>
> This code is double swapping. The calling code swaps (bit settings),
> regmap calls this function, where the word is swapped again.
>
> Guenter
>