[PATCH v2 0/2] hwmon: (pmbus/tps53679) Select page 0 for single-page parts

[PATCH v2 0/2] hwmon: (pmbus/tps53679) Select page 0 for single-page parts

[Pradhan, Sanman]

From: Sanman Pradhan <psanman@juniper.net>

For single-page TPS53676 and TPS536C7 configurations the PAGE register is
never normalised: pmbus_set_page() only writes PAGE when info->pages > 1,
so a page left selected by the boot firmware persists and telemetry is
read from the wrong page. Select page 0 explicitly in the two identify
routines.

Patch 1 fixes the pre-existing TPS53676 issue and carries Fixes/stable
tags. Patch 2 fixes the newly added TPS536C7 support; the TPS536C7 series
has already been applied by the hwmon maintainer but is not yet in a
released kernel, so patch 2 carries no stable tag.

These patches are based on top of the previously submitted TPS536C7
series.

Changes in v2:
- Drop the PAGE read-back/verify; just write PAGE = 0.

Sanman Pradhan (2):
  hwmon: (pmbus/tps53679) Select page 0 for single-page TPS53676
  hwmon: (pmbus/tps53679) Select page 0 for single-page TPS536C7

 drivers/hwmon/pmbus/tps53679.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

-- 
2.34.1

[PATCH v2 1/2] hwmon: (pmbus/tps53679) Select page 0 for single-page TPS53676

[Pradhan, Sanman]

From: Sanman Pradhan <psanman@juniper.net>

tps53676_identify() derives the number of PMBus pages but does not
ensure that page 0 is selected for single-page configurations.
pmbus_set_page() does not update the PAGE register when info->pages is
1, so if boot firmware leaves PAGE set to another value subsequent
register accesses may target the wrong page.

For single-page devices, select page 0 explicitly.

Fixes: cb3d37b59012 ("hwmon: (pmbus/tps53679) Add support for TI TPS53676")
Cc: stable@vger.kernel.org
Signed-off-by: Sanman Pradhan <psanman@juniper.net>
---
 drivers/hwmon/pmbus/tps53679.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/hwmon/pmbus/tps53679.c b/drivers/hwmon/pmbus/tps53679.c
index dcd4250b679d..4f91b0a43ad0 100644
--- a/drivers/hwmon/pmbus/tps53679.c
+++ b/drivers/hwmon/pmbus/tps53679.c
@@ -246,6 +246,15 @@ static int tps53676_identify(struct i2c_client *client,
 	if (phases_b > 0) {
 		info->pages = 2;
 		info->phases[1] = phases_b;
+	} else {
+		/*
+		 * pmbus_set_page() does not update the PAGE register on
+		 * single-page devices, so select page 0 explicitly in case
+		 * the boot firmware left the device on another page.
+		 */
+		ret = i2c_smbus_write_byte_data(client, PMBUS_PAGE, 0);
+		if (ret < 0)
+			return ret;
 	}
 
 	return 0;
-- 
2.34.1

Re: [PATCH v2 1/2] hwmon: (pmbus/tps53679) Select page 0 for single-page TPS53676

[Guenter Roeck]

On Wed, Sep 16, 2026 at 11:54:17PM +0000, Pradhan, Sanman wrote:
> From: Sanman Pradhan <psanman@juniper.net>
> 
> tps53676_identify() derives the number of PMBus pages but does not
> ensure that page 0 is selected for single-page configurations.
> pmbus_set_page() does not update the PAGE register when info->pages is
> 1, so if boot firmware leaves PAGE set to another value subsequent
> register accesses may target the wrong page.
> 
> For single-page devices, select page 0 explicitly.
> 
> Fixes: cb3d37b59012 ("hwmon: (pmbus/tps53679) Add support for TI TPS53676")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sanman Pradhan <psanman@juniper.net>

Applied.

Thanks,
Guenter

[PATCH v2 2/2] hwmon: (pmbus/tps53679) Select page 0 for single-page TPS536C7

[Pradhan, Sanman]

From: Sanman Pradhan <psanman@juniper.net>

tps536c7_identify() sets info->pages to 1 for a single-channel part and
then accesses page 0 (writing PMBUS_PHASE) without ensuring PAGE is
actually 0. pmbus_set_page() does not update the PAGE register when
info->pages is 1, so if boot firmware left PAGE set to another value the
PHASE writes and subsequent telemetry may target the wrong page.

Select page 0 explicitly before configuring PHASE.

Signed-off-by: Sanman Pradhan <psanman@juniper.net>
---
 drivers/hwmon/pmbus/tps53679.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/hwmon/pmbus/tps53679.c b/drivers/hwmon/pmbus/tps53679.c
index 4f91b0a43ad0..df21bc5aa128 100644
--- a/drivers/hwmon/pmbus/tps53679.c
+++ b/drivers/hwmon/pmbus/tps53679.c
@@ -284,6 +284,17 @@ static int tps536c7_identify(struct i2c_client *client,
 	 */
 	info->pages = phases_b ? 2 : 1;
 
+	/*
+	 * pmbus_set_page() does not update the PAGE register on single-page
+	 * devices, so select page 0 explicitly in case the boot firmware
+	 * left the device on another page.
+	 */
+	if (info->pages == 1) {
+		ret = i2c_smbus_write_byte_data(client, PMBUS_PAGE, 0);
+		if (ret < 0)
+			return ret;
+	}
+
 	/*
 	 * With info->phases[] left unset the PMBus core never programs the
 	 * PHASE selector, so make sure each page reports the aggregate
-- 
2.34.1

Re: [PATCH v2 2/2] hwmon: (pmbus/tps53679) Select page 0 for single-page TPS536C7

[Guenter Roeck]

On Wed, Sep 16, 2026 at 11:54:21PM +0000, Pradhan, Sanman wrote:
> From: Sanman Pradhan <psanman@juniper.net>
> 
> tps536c7_identify() sets info->pages to 1 for a single-channel part and
> then accesses page 0 (writing PMBUS_PHASE) without ensuring PAGE is
> actually 0. pmbus_set_page() does not update the PAGE register when
> info->pages is 1, so if boot firmware left PAGE set to another value the
> PHASE writes and subsequent telemetry may target the wrong page.
> 
> Select page 0 explicitly before configuring PHASE.
> 
> Signed-off-by: Sanman Pradhan <psanman@juniper.net>

Applied.

Thanks,
Guenter