linux-kernel - Re: [PATCH] hwmod: (pmbus) disable PEC if not enabled

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Date:   Tue, 19 Apr 2022 22:10:46 +0000
From:   wujek dev <dev_public@...ek.eu>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmod: (pmbus) disable PEC if not enabled

------- Original Message -------
On Wednesday, April 20th, 2022 at 00:00, Guenter Roeck <linux@...ck-us.net> wrote:
>
>
> On 4/19/22 13:53, Adam Wujek wrote:
>
> > Explicitly disable PEC when the client does not support it.
> > Without the explicit disable, when the device with the PEC support is removed
> > later when a device without PEC support is inserted into the same address,
> > the driver uses the old value of client->flags which contains the I2C_CLIENT_PEC
> > flag. As a consequence the PEC is used when it should not.
>
>
> How can that happen ? I would assume the I2C device gets deleted and re-created
> in that case, which should clear the PEC flag.
>
> Guenter
In my case it was when I unloaded the driver for the I2C slave, changed the advertised PEC value in PMBUS_CAPABILITY register on slave. Then loaded the driver. When the switch was from disable->enable it worked as expected (this case was already covered), but when the PEC was set in the slave from enabled->disabled it was still using PEC to communicate.

Adam
>
> > Signed-off-by: Adam Wujek dev_public@...ek.eu
> > ---
> > drivers/hwmon/pmbus/pmbus_core.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> > index 82c3754e21e3..f8ca36759b0a 100644
> > --- a/drivers/hwmon/pmbus/pmbus_core.c
> > +++ b/drivers/hwmon/pmbus/pmbus_core.c
> > @@ -2014,6 +2014,8 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
> > ret = i2c_smbus_read_byte_data(client, PMBUS_CAPABILITY);
> > if (ret >= 0 && (ret & PB_CAPABILITY_ERROR_CHECK))
> > client->flags |= I2C_CLIENT_PEC;
> > + else
> > + client->flags &= ~I2C_CLIENT_PEC;
> >
> > pmbus_clear_faults(client);
> >
> > --
> > 2.17.1