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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Adam Wujek <dev_public@wujek.eu>,
        Guenter Roeck <linux@roeck-us.net>
Subject: [PATCH 5.17 056/140] hwmon: (pmbus) disable PEC if not enabled
Date:   Tue, 10 May 2022 15:07:26 +0200
Message-Id: <20220510130743.221225564@linuxfoundation.org>
In-Reply-To: <20220510130741.600270947@linuxfoundation.org>
References: <20220510130741.600270947@linuxfoundation.org>
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From: Adam Wujek <dev_public@wujek.eu>

commit 75d2b2b06bd8407d03a3f126bc8b95eb356906c7 upstream.

Explicitly disable PEC when the client does not support it.
The problematic scenario is the following. A device with enabled PEC
support is up and running and a kernel driver is loaded.
Then the driver is unloaded (or device unbound), the HW device
is reconfigured externally (e.g. by i2cset) to advertise itself as not
supporting PEC. Without a new code, at the second load of the driver
(or bind) the "flags" variable is not updated to avoid PEC usage. As a
consequence the further communication with the device is done with
the PEC enabled, which is wrong and may fail.

The implementation first disable the I2C_CLIENT_PEC flag, then the old
code enable it if needed.

Fixes: 4e5418f787ec ("hwmon: (pmbus_core) Check adapter PEC support")
Signed-off-by: Adam Wujek <dev_public@wujek.eu>
Link: https://lore.kernel.org/r/20220420145059.431061-1-dev_public@wujek.eu
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/hwmon/pmbus/pmbus_core.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -2326,6 +2326,9 @@ static int pmbus_init_common(struct i2c_
 		data->has_status_word = true;
 	}
 
+	/* Make sure PEC is disabled, will be enabled later if needed */
+	client->flags &= ~I2C_CLIENT_PEC;
+
 	/* Enable PEC if the controller and bus supports it */
 	if (!(data->flags & PMBUS_NO_CAPABILITY)) {
 		ret = i2c_smbus_read_byte_data(client, PMBUS_CAPABILITY);