netdev - Re: [patch net-next v2 4/6] mlxsw: core: Implement temperature hwmon interface

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Date:	Sun, 29 Nov 2015 11:49:18 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Or Gerlitz <gerlitz.or@...il.com>
Cc:	Linux Netdev List <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>, idosch@...lanox.com,
	Elad Raz <eladr@...lanox.com>, yotamg@...lanox.com
Subject: Re: [patch net-next v2 4/6] mlxsw: core: Implement temperature hwmon
 interface

Sun, Nov 29, 2015 at 10:04:07AM CET, gerlitz.or@...il.com wrote:
>[..]
>> +enum mlxsw_hwmon_attr_type {
>> +       MLXSW_HWMON_ATTR_TYPE_TEMP,
>> +       MLXSW_HWMON_ATTR_TYPE_TEMP_MAX,
>> +};
>> +
>> +static void mlxsw_hwmon_attr_add(struct mlxsw_hwmon *mlxsw_hwmon,
>> +                                enum mlxsw_hwmon_attr_type attr_type,
>> +                                unsigned int type_index, unsigned int num) {
>> +       struct mlxsw_hwmon_attr *mlxsw_hwmon_attr;
>> +       unsigned int attr_index;
>> +
>> +       attr_index = mlxsw_hwmon->attrs_count;
>> +       mlxsw_hwmon_attr = &mlxsw_hwmon->hwmon_attrs[attr_index];
>> +
>> +       switch (attr_type) {
>> +       case MLXSW_HWMON_ATTR_TYPE_TEMP:
>> +               mlxsw_hwmon_attr->dev_attr.show = mlxsw_hwmon_temp_show;
>> +               mlxsw_hwmon_attr->dev_attr.attr.mode = S_IRUGO;
>> +               snprintf(mlxsw_hwmon_attr->name, sizeof(mlxsw_hwmon_attr->name),
>> +                        "temp%u_input", num + 1);
>> +               break;
>> +       case MLXSW_HWMON_ATTR_TYPE_TEMP_MAX:
>> +               mlxsw_hwmon_attr->dev_attr.show = mlxsw_hwmon_temp_max_show;
>> +               mlxsw_hwmon_attr->dev_attr.attr.mode = S_IRUGO;
>> +               snprintf(mlxsw_hwmon_attr->name, sizeof(mlxsw_hwmon_attr->name),
>> +                        "temp%u_highest", num + 1);
>> +               break;
>> +       default:
>> +               BUG();
>
>Guys, do we really have to crash the whole system just b/c somehow an unknown
>value propagated here during **init** time?
>
>I don't think so.

"default" case simply *cannot* happen. If it happens, it is a stack
corruption or some other fatal problem. I believe that BUG is
appropriate at these cases.

>
>> +
>> +       mlxsw_hwmon_attr->type_index = type_index;
>> +       mlxsw_hwmon_attr->hwmon = mlxsw_hwmon;
>> +       mlxsw_hwmon_attr->dev_attr.attr.name = mlxsw_hwmon_attr->name;
>> +       sysfs_attr_init(&mlxsw_hwmon_attr->dev_attr.attr);
>> +
>> +       mlxsw_hwmon->attrs[attr_index] = &mlxsw_hwmon_attr->dev_attr.attr;
>> +       mlxsw_hwmon->attrs_count++;
>> +}
>> +
>
>[...]
>> +int mlxsw_hwmon_init(struct mlxsw_core *mlxsw_core,
>> +                    const struct mlxsw_bus_info *mlxsw_bus_info,
>> +                    struct mlxsw_hwmon **p_hwmon)
>> +{
>> +       struct mlxsw_hwmon *mlxsw_hwmon;
>> +       struct device *hwmon_dev;
>> +       int err;
>> +
>> +       mlxsw_hwmon = kzalloc(sizeof(*mlxsw_hwmon), GFP_KERNEL);
>> +       if (!mlxsw_hwmon)
>> +               return -ENOMEM;
>> +       mlxsw_hwmon->core = mlxsw_core;
>> +       mlxsw_hwmon->bus_info = mlxsw_bus_info;
>> +
>> +       err = mlxsw_hwmon_temp_init(mlxsw_hwmon);
>> +       if (err)
>> +               goto err_temp_init;
>> +
>> +       mlxsw_hwmon->groups[0] = &mlxsw_hwmon->group;
>> +       mlxsw_hwmon->group.attrs = mlxsw_hwmon->attrs;
>> +
>> +       hwmon_dev = devm_hwmon_device_register_with_groups(mlxsw_bus_info->dev,
>> +                                                          "mlxsw",
>> +                                                          mlxsw_hwmon,
>> +                                                          mlxsw_hwmon->groups);
>> +       if (IS_ERR(hwmon_dev)) {
>> +               err = PTR_ERR(hwmon_dev);
>> +               goto err_hwmon_register;
>> +       }
>> +
>> +       mlxsw_hwmon->hwmon_dev = hwmon_dev;
>> +       *p_hwmon = mlxsw_hwmon;
>> +       return 0;
>> +
>> +err_hwmon_register:
>> +err_temp_init:
>> +       kfree(mlxsw_hwmon);
>> +       return err;
>> +}
>> +
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