linux-kernel - [v3 PATCH] hwmon: (pmbus) disable PEC if not enabled

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Message-ID: <20220420145059.431061-1-dev_public@wujek.eu>
Date:   Wed, 20 Apr 2022 14:51:25 +0000
From:   Adam Wujek <dev_public@...ek.eu>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Adam Wujek <dev_public@...ek.eu>,
        Guenter Roeck <linux@...ck-us.net>,
        Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [v3 PATCH] hwmon: (pmbus) disable PEC if not enabled

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.

Signed-off-by: Adam Wujek <dev_public@...ek.eu>
---
Notes:
    Changes in v2:
    - Rebase to the latest kernel
    - Update commit message

    Changes in v3:
    - Rework the patch, disable the flag first, then enable if needed.
      Adding three else statements to disable the flag will make the code
      less readable.
    - Update commit message

 drivers/hwmon/pmbus/pmbus_core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index b2618b1d529e..d93574d6a1fb 100644
--- 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_client *client, struct pmbus_data *data,
 		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);
--
2.25.1