On 4/28/25 15:13, Pawel Dembicki wrote:
Implement support for setting the VOUT_SCALE_LOOP PMBus register
based on an optional device tree property "voltage-scale-loop".
This allows the driver to provide the correct VOUT value depending
on the feedback voltage divider configuration for chips where the
bootloader does not configure the voltage scale.
Signed-off-by: Pawel Dembicki <paweldembicki@xxxxxxxxx>
---
drivers/hwmon/pmbus/mpq8785.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/drivers/hwmon/pmbus/mpq8785.c b/drivers/hwmon/pmbus/mpq8785.c
index e6a643856f08..6e2325d7f37b 100644
--- a/drivers/hwmon/pmbus/mpq8785.c
+++ b/drivers/hwmon/pmbus/mpq8785.c
@@ -78,6 +78,8 @@ static int mpq8785_probe(struct i2c_client *client)
struct device *dev = &client->dev;
struct pmbus_driver_info *info;
enum chips chip_id;
+ u32 voltage_scale;
+ int ret;
info = devm_kmemdup(dev, &mpq8785_info, sizeof(*info), GFP_KERNEL);
if (!info)
@@ -105,6 +107,14 @@ static int mpq8785_probe(struct i2c_client *client)
return -ENODEV;
}
+ if (!of_property_read_u32(dev->of_node, "voltage-scale-loop",
+ &voltage_scale)) {
+ ret = i2c_smbus_write_word_data(client, PMBUS_VOUT_SCALE_LOOP,
+ voltage_scale);
Per PMBus specification this value can be in any supported scale.
Also, the chips do not support the full 16-bit value range. I see 10 bit for
mpq8785 and mpm3695, 7 bit for mp2853, and 12 bit for MPM82504. There will
have to be some device specific range check.
I don't understand the units. The devicetree document talks about
VOUT_SCALE_LOOP = VFB / VOUT * 1000, but I don't see how that translates
into chip values. For MPM82504, the datasheet says 1 LSB=2mV. For mpm3695
it is 0.001/LSB. I have no idea how that is supposed to translate to the
units suggested in the property patch.
Either case, I think the property needs to be something generic that is well
defined. Maybe "pmbus,voltage-scale-loop", but I really don't know what would
be acceptable for DT maintainers.
Guenter
