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Sender: Guenter Roeck <groeck7@gmail.com>
Date: Thu, 23 May 2024 07:19:59 -0700
From: Guenter Roeck <linux@roeck-us.net>
To: Radu Sabau <radu.sabau@analog.com>
Cc: Jean Delvare <jdelvare@suse.com>, Jonathan Corbet <corbet@lwn.net>,
	linux-hwmon@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] drivers: hwmon: max31827: Add PEC support
Message-ID: <e52a86de-ead6-40d3-b652-461a90bd5942@roeck-us.net>
References: <20240523121057.5689-1-radu.sabau@analog.com>
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In-Reply-To: <20240523121057.5689-1-radu.sabau@analog.com>

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@analog.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/

Guenter