linux-kernel - [PATCH 1/2] usb: typec: maxim_contaminant: disable low power mode when reading comparator values

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Message-Id: <20250814-fix-upstream-contaminant-v1-1-801ce8089031@google.com>
Date: Thu, 14 Aug 2025 19:34:09 -0700
From: Amit Sunil Dhamne via B4 Relay <devnull+amitsd.google.com@...nel.org>
To: Heikki Krogerus <heikki.krogerus@...ux.intel.com>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Badhri Jagan Sridharan <badhri@...gle.com>, 
 Guenter Roeck <linux@...ck-us.net>
Cc: linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, 
 stable@...r.kernel.org, RD Babiera <rdbabiera@...gle.com>, 
 Kyle Tso <kyletso@...gle.com>, 
 André Draszik <andre.draszik@...aro.org>, 
 Peter Griffin <peter.griffin@...aro.org>, 
 Tudor Ambarus <tudor.ambarus@...aro.org>, 
 Amit Sunil Dhamne <amitsd@...gle.com>
Subject: [PATCH 1/2] usb: typec: maxim_contaminant: disable low power mode
 when reading comparator values

From: Amit Sunil Dhamne <amitsd@...gle.com>

Low power mode is enabled when reading CC resistance as part of
`max_contaminant_read_resistance_kohm()` and left in that state.
However, it's supposed to work with 1uA current source. To read CC
comparator values current source is changed to 80uA. This causes a storm
of CC interrupts as it (falsely) detects a potential contaminant. To
prevent this, disable low power mode current sourcing before reading
comparator values.

Fixes: 02b332a06397 ("usb: typec: maxim_contaminant: Implement check_contaminant callback")
Signed-off-by: Amit Sunil Dhamne <amitsd@...gle.com>
Reviewed-by: Badhri Jagan Sridharan <badhri@...gle.com>
---
 drivers/usb/typec/tcpm/maxim_contaminant.c | 5 +++++
 drivers/usb/typec/tcpm/tcpci_maxim.h       | 1 +
 2 files changed, 6 insertions(+)

diff --git a/drivers/usb/typec/tcpm/maxim_contaminant.c b/drivers/usb/typec/tcpm/maxim_contaminant.c
index 0cdda06592fd3cc34e2179ccd49ef677f8ec9792..818cfe226ac7716de2fcbce205c67ea16acba592 100644
--- a/drivers/usb/typec/tcpm/maxim_contaminant.c
+++ b/drivers/usb/typec/tcpm/maxim_contaminant.c
@@ -188,6 +188,11 @@ static int max_contaminant_read_comparators(struct max_tcpci_chip *chip, u8 *ven
 	if (ret < 0)
 		return ret;
 
+	/* Disable low power mode */
+	ret = regmap_update_bits(regmap, TCPC_VENDOR_CC_CTRL2, CCLPMODESEL,
+				 FIELD_PREP(CCLPMODESEL,
+					    LOW_POWER_MODE_DISABLE));
+
 	/* Sleep to allow comparators settle */
 	usleep_range(5000, 6000);
 	ret = regmap_update_bits(regmap, TCPC_TCPC_CTRL, TCPC_TCPC_CTRL_ORIENTATION, PLUG_ORNT_CC1);
diff --git a/drivers/usb/typec/tcpm/tcpci_maxim.h b/drivers/usb/typec/tcpm/tcpci_maxim.h
index 76270d5c283880dc49b13cabe7d682f2c2bf15fe..b33540a42a953dc6d8197790ee4af3b6f52791ce 100644
--- a/drivers/usb/typec/tcpm/tcpci_maxim.h
+++ b/drivers/usb/typec/tcpm/tcpci_maxim.h
@@ -21,6 +21,7 @@
 #define CCOVPDIS                                BIT(6)
 #define SBURPCTRL                               BIT(5)
 #define CCLPMODESEL                             GENMASK(4, 3)
+#define LOW_POWER_MODE_DISABLE                  0
 #define ULTRA_LOW_POWER_MODE                    1
 #define CCRPCTRL                                GENMASK(2, 0)
 #define UA_1_SRC                                1

-- 
2.51.0.rc1.167.g924127e9c0-goog