On 9/10/20 10:08 AM, Chu Lin wrote: > Problem: > We use voltage dividers so that the voltage presented at the voltage > sense pins is confusing. We might need to convert these readings to more > meaningful readings given the voltage divider. > > Solution: > Read the voltage divider resistance from dts and convert the voltage > reading to a more meaningful reading. > > Testing: > max20730 with voltage divider > > Signed-off-by: Chu Lin <linchuy...@google.com> > --- > drivers/hwmon/pmbus/max20730.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/drivers/hwmon/pmbus/max20730.c b/drivers/hwmon/pmbus/max20730.c > index c0bb05487e0e..4b56810fa894 100644 > --- a/drivers/hwmon/pmbus/max20730.c > +++ b/drivers/hwmon/pmbus/max20730.c > @@ -29,6 +29,7 @@ struct max20730_data { > struct pmbus_driver_info info; > struct mutex lock; /* Used to protect against parallel writes */ > u16 mfr_devset1; > + u32 vout_voltage_divider[2]; > }; > > #define to_max20730_data(x) container_of(x, struct max20730_data, info) > @@ -111,6 +112,12 @@ static int max20730_read_word_data(struct i2c_client > *client, int page, > max_c = max_current[data->id][(data->mfr_devset1 >> 5) & 0x3]; > ret = val_to_direct(max_c, PSC_CURRENT_OUT, info); > break; > + case PMBUS_READ_VOUT: > + ret = pmbus_read_word_data(client, page, phase, reg);
if (ret < 0) return ret; > + if (data->vout_voltage_divider[0] && > data->vout_voltage_divider[1]) > + ret = DIV_ROUND_CLOSEST(ret * > data->vout_voltage_divider[1], > + data->vout_voltage_divider[0]); With no range checks, ret * data->vout_voltage_divider[1] can easily overflow if vout_voltage_divider[] is larger than 0xffff. Also, the pmbus core does not expect register values larger than 0xffff (it typecasts the returned value explicitly to u16). [ Grumble. The PMBus specification has VOUT_SCALE commands to handle this situation. It is quite annoying that this chip does not support it. ] Guenter > + break; > default: > ret = -ENODATA; > break; > @@ -329,6 +336,15 @@ static int max20730_probe(struct i2c_client *client, > data->id = chip_id; > mutex_init(&data->lock); > memcpy(&data->info, &max20730_info[chip_id], sizeof(data->info)); > + if (of_property_read_u32_array(client->dev.of_node, > "vout-voltage-divider", > + data->vout_voltage_divider, > + ARRAY_SIZE(data->vout_voltage_divider)) > != 0) > + memset(data->vout_voltage_divider, 0, > sizeof(data->vout_voltage_divider)); > + if (data->vout_voltage_divider[1] < data->vout_voltage_divider[0]) { > + dev_err(dev, > + "The total resistance of voltage divider is less than > output resistance\n"); > + return -ENODEV; > + } > > ret = i2c_smbus_read_word_data(client, MAX20730_MFR_DEVSET1); > if (ret < 0) >