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Subject: Re: [PATCH] hwmon: (pmbus) Expose PEC debugfs attribute
To:     Andrew Jeffery <andrew@aj.id.au>, linux-hwmon@vger.kernel.org
Cc:     jdelvare@suse.com, openbmc@lists.ozlabs.org,
        linux-kernel@vger.kernel.org
References: <20200909132411.2906159-1-andrew@aj.id.au>
From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <4f2de881-1391-b1b1-18b3-8d3a06653da9@roeck-us.net>
Date:   Wed, 9 Sep 2020 08:31:05 -0700
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On 9/9/20 6:24 AM, Andrew Jeffery wrote:
> Enable runtime debug control of whether the PEC byte is exchanged with
> the PMBus device.
> 
> Some manufacturers have asked for the PEC to be disabled as part of
> debugging driver communication issues with devices.
> 
> Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
> ---
>  drivers/hwmon/pmbus/pmbus_core.c | 39 ++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index 44535add3a4a..51c8502b35e9 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -2346,6 +2346,42 @@ static int pmbus_debugfs_get_status(void *data, u64 *val)
>  DEFINE_DEBUGFS_ATTRIBUTE(pmbus_debugfs_ops_status, pmbus_debugfs_get_status,
>  			 NULL, "0x%04llx\n");
>  
> +static int pmbus_debugfs_get_pec(void *data, u64 *val)
> +{
> +	struct i2c_client *client = data;
> +
> +	*val = !!(client->flags & I2C_CLIENT_PEC);
> +
> +	return 0;
> +}
> +
> +static int pmbus_debugfs_set_pec(void *data, u64 val)
> +{
> +	int rc;
> +	struct i2c_client *client = data;
> +
> +	if (!val) {
> +		client->flags &= ~I2C_CLIENT_PEC;
> +		return 0;
> +	}
> +
> +	if (val != 1)
> +		return -EINVAL;
> +
> +	rc = i2c_smbus_read_byte_data(client, PMBUS_CAPABILITY);
> +	if (rc < 0)
> +		return rc;
> +
> +	if (!(rc & PB_CAPABILITY_ERROR_CHECK))
> +		return -ENOTSUPP;

WARNING: ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP

> +
> +	client->flags |= I2C_CLIENT_PEC;
> +
> +	return 0;
> +}
> +DEFINE_DEBUGFS_ATTRIBUTE(pmbus_debugfs_ops_pec, pmbus_debugfs_get_pec,
> +			 pmbus_debugfs_set_pec, "0x%1llu\n");

ERROR: Prefixing 0x with decimal output is defective

(since the displayed value is a boolean, it is also quite useless).

> +
>  static int pmbus_init_debugfs(struct i2c_client *client,
>  			      struct pmbus_data *data)
>  {
> @@ -2374,6 +2410,9 @@ static int pmbus_init_debugfs(struct i2c_client *client,
>  	if (!entries)
>  		return -ENOMEM;
>  
> +	debugfs_create_file("pec", 0664, data->debugfs, client,
> +			    &pmbus_debugfs_ops_pec);
> +
>  	for (i = 0; i < data->info->pages; ++i) {
>  		/* Check accessibility of status register if it's not page 0 */
>  		if (!i || pmbus_check_status_register(client, i)) {
>