linux-kernel - Re: [PATCH v2] drivers: hwmon: max31827: Add PEC support

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Message-ID: <5bb5b291-ec6c-4233-b2f2-bf7f1ba74d24@roeck-us.net>
Date: Fri, 24 May 2024 06:20:47 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Nuno Sá <noname.nuno@...il.com>,
 Radu Sabau <radu.sabau@...log.com>
Cc: Jean Delvare <jdelvare@...e.com>, Jonathan Corbet <corbet@....net>,
 linux-hwmon@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drivers: hwmon: max31827: Add PEC support

On 5/24/24 00:00, Nuno Sá wrote:
> On Thu, 2024-05-23 at 07:19 -0700, Guenter Roeck wrote:
>> On Thu, May 23, 2024 at 03:10:56PM +0300, Radu Sabau wrote:
>>> Add support for PEC by attaching PEC attribute to the i2c device.
>>> Add pec_store and pec_show function for accesing the "pec" file.
>>>
>>> Signed-off-by: Radu Sabau <radu.sabau@...log.com>
>>> ---
>>
>> Change log missing.
>>
>>>   Documentation/hwmon/max31827.rst | 13 +++++--
>>>   drivers/hwmon/max31827.c         | 64 ++++++++++++++++++++++++++++++++
>>>   2 files changed, 74 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/Documentation/hwmon/max31827.rst b/Documentation/hwmon/max31827.rst
>>> index 44ab9dc064cb..9c11a9518c67 100644
>>> --- a/Documentation/hwmon/max31827.rst
>>> +++ b/Documentation/hwmon/max31827.rst
>>> @@ -131,7 +131,14 @@ The Fault Queue bits select how many consecutive temperature
>>> faults must occur
>>>   before overtemperature or undertemperature faults are indicated in the
>>>   corresponding status bits.
>>>   
>>> -Notes
>>> ------
>>> +PEC Support
>>> +-----------
>>> +
>>> +When reading a register value, the PEC byte is computed and sent by the chip.
>>> +
>>> +PEC on word data transaction respresents a signifcant increase in bandwitdh
>>> +usage (+33% for both write and reads) in normal conditions.
>>>   
>>> -PEC is not implemented.
>>> +Since this operation implies there will be an extra delay to each
>>> +transaction, PEC can be disabled or enabled through sysfs.
>>> +Just write 1  to the "pec" file for enabling PEC and 0 for disabling it.
>>> diff --git a/drivers/hwmon/max31827.c b/drivers/hwmon/max31827.c
>>> index f8a13b30f100..e86f8890ee72 100644
>>> --- a/drivers/hwmon/max31827.c
>>> +++ b/drivers/hwmon/max31827.c
>>> @@ -24,6 +24,7 @@
>>>   
>>>   #define MAX31827_CONFIGURATION_1SHOT_MASK	BIT(0)
>>>   #define MAX31827_CONFIGURATION_CNV_RATE_MASK	GENMASK(3, 1)
>>> +#define MAX31827_CONFIGURATION_PEC_EN_MASK	BIT(4)
>>>   #define MAX31827_CONFIGURATION_TIMEOUT_MASK	BIT(5)
>>>   #define MAX31827_CONFIGURATION_RESOLUTION_MASK	GENMASK(7, 6)
>>>   #define MAX31827_CONFIGURATION_ALRM_POL_MASK	BIT(8)
>>> @@ -475,6 +476,54 @@ static ssize_t temp1_resolution_store(struct device *dev,
>>>   
>>>   static DEVICE_ATTR_RW(temp1_resolution);
>>>   
>>> +static ssize_t pec_show(struct device *dev, struct device_attribute *devattr,
>>> +			char *buf)
>>> +{
>>> +	struct i2c_client *client = to_i2c_client(dev);
>>> +
>>> +	return scnprintf(buf, PAGE_SIZE, "%d\n", !!(client->flags &
>>> I2C_CLIENT_PEC));
>>> +}
>>> +
>>> +static ssize_t pec_store(struct device *dev, struct device_attribute *devattr,
>>> +			 const char *buf, size_t count)
>>> +{
>>> +	struct max31827_state *st = dev_get_drvdata(dev);
>>> +	struct i2c_client *client = to_i2c_client(dev);
>>> +	unsigned int val;
>>> +	int err;
>>> +
>>> +	err = kstrtouint(buf, 10, &val);
>>> +	if (err < 0)
>>> +		return err;
>>> +
>>> +	switch (val) {
>>> +	case 0:
>>> +		err = regmap_update_bits(st->regmap, MAX31827_CONFIGURATION_REG,
>>> +					 MAX31827_CONFIGURATION_PEC_EN_MASK,
>>> +					 val);
>>
>> While correct, this is misleading. Should write 0.
>>
>>> +		if (err)
>>> +			return err;
>>> +
>>> +		client->flags &= ~I2C_CLIENT_PEC;
>>> +		break;
>>> +	case 1:
>>> +		err = regmap_update_bits(st->regmap, MAX31827_CONFIGURATION_REG,
>>> +					 MAX31827_CONFIGURATION_PEC_EN_MASK,
>>> +					 val);
>>
>> This is wrong. s/val/MAX31827_CONFIGURATION_PEC_EN_MASK/
>>
>>
> 
> Then, maybe use regmap_set_bits()...

Good point, and regmap_clear_bits() above.

Guenter

> 
> - Nuno Sá
>