[PATCH 6.18 233/641] hwmon: (pmbus/mpq8785) fix VOUT_MODE mismatch during identification

Greg Kroah-Hartman
2026-02-25T01:46:21Z

6.18-stable review patch. If anyone has any objections, please let me know.

------------------

From: Carl Lee <carl.lee@amd.com>

[ Upstream commit 9e33c1dba22431bea9b2bf48adf56859e52fc7ec ]

When MPQ8785 reports VOUT_MODE as VID mode, mpq8785_identify()
configures the driver for direct mode. The subsequent
pmbus_identify_common() check then fails due to a mismatch
between the reported mode and the configured mode, causing
device initialization to fail.

Override the reported VOUT_MODE to direct mode to keep the
driver configuration consistent with the reported mode and
allow successful device initialization.

This does not change how voltages are interpreted, but avoids
a false identification failure caused by mismatched mode
handling.

Fixes: f20b4a931130c ("hwmon: Add driver for MPS MPQ8785 Synchronous Step-Down Converter")
Signed-off-by: Carl Lee <carl.lee@amd.com>
Link: https://lore.kernel.org/r/20260210-dt-bindings-hwmon-pmbus-mpq8785-add-mpq8786-support-v3-1-84636ccfe76f@amd.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/hwmon/pmbus/mpq8785.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)

diff --git a/drivers/hwmon/pmbus/mpq8785.c b/drivers/hwmon/pmbus/mpq8785.c
index 1f56aaf4dde80..87bd039c77b9b 100644
--- a/drivers/hwmon/pmbus/mpq8785.c
+++ b/drivers/hwmon/pmbus/mpq8785.c
@@ -47,6 +47,33 @@ static int mpq8785_identify(struct i2c_client *client,
return 0;
};

+static int mpq8785_read_byte_data(struct i2c_client *client, int page, int reg)
+{
+ int ret;
+
+ switch (reg) {
+ case PMBUS_VOUT_MODE:
+ ret = pmbus_read_byte_data(client, page, reg);
+ if (ret < 0)
+ return ret;
+
+ if ((ret >> 5) == 1) {
+ /*
+ * The MPQ8785 chip reports VOUT_MODE as VID mode, but the driver
+ * treats VID as direct mode. Without this, identification would fail
+ * due to mode mismatch.
+ * This override ensures the reported mode matches the driver
+ * configuration, allowing successful initialization.
+ */
+ return PB_VOUT_MODE_DIRECT;
+ }
+
+ return ret;
+ default:
+ return -ENODATA;
+ }
+}
+
static int mpm82504_read_word_data(struct i2c_client *client, int page,
int phase, int reg)
{
@@ -129,6 +156,7 @@ static int mpq8785_probe(struct i2c_client *client)
break;
case mpq8785:
info->identify = mpq8785_identify;
+ info->read_byte_data = mpq8785_read_byte_data;
break;
default:
return -ENODEV;
--
2.51.0