linux-kernel - Re: [PATCH v4 2/2] hwmon: (max6639) : Add hwmon attributes for fan and pwm

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Date: Thu, 13 Jun 2024 06:44:06 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Naresh Solanki <naresh.solanki@...ements.com>
Cc: Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] hwmon: (max6639) : Add hwmon attributes for fan
 and pwm

On 6/13/24 02:51, Naresh Solanki wrote:
...
>>
>>> +     switch (attr) {
>>> +     case hwmon_fan_pulses:
>>> +             if (val <= 0 || val > 5)
>>> +                     return -EINVAL;
>>> +
>>> +             /* Set Fan pulse per revolution */
>>> +             err = max6639_set_ppr(data, channel, val);
>>> +             if (err < 0)
>>> +                     return err;
>>> +
>>> +             data->ppr[channel] = val;
>>
>> Needs mutex protection to avoid inconsistencies due to concurrent writes.
> This is single i2c access. Still we need mutex protection here ?

In this case, the mutex doesn't protect the i2c access, it protects the
consistency between the chip configuration and the information stored
in data->ppr[].

CPU1			CPU2
[val==1]		[val!=1]

max6639_set_ppr();
			max6639_set_ppr();
			data->ppr[channel] = val;
data->ppr[channel] = val;

The alternative would be to not cache ppr and read it from the regmap cache
when needed.

Guenter