linux-kernel - Re: [PATCH 1/2] drivers: hwmon: max31827: Add PEC support

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Date: Wed, 22 May 2024 15:08:51 +0200
From: Nuno Sá <noname.nuno@...il.com>
To: Radu Sabau <radu.sabau@...log.com>, Jean Delvare <jdelvare@...e.com>, 
 Guenter Roeck <linux@...ck-us.net>, Jonathan Corbet <corbet@....net>,
 linux-hwmon@...r.kernel.org,  linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] drivers: hwmon: max31827: Add PEC support

On Wed, 2024-05-22 at 15:39 +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>
> ---
>  Documentation/hwmon/max31827.rst | 13 ++++-
>  drivers/hwmon/max31827.c         | 95 +++++++++++++++++++++++++++-----
>  2 files changed, 92 insertions(+), 16 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..16a1524413db 100644
> --- a/drivers/hwmon/max31827.c
> +++ b/drivers/hwmon/max31827.c
> @@ -11,19 +11,20 @@
>  #include <linux/hwmon.h>
>  #include <linux/i2c.h>
>  #include <linux/mutex.h>
> -#include <linux/of_device.h>
>  #include <linux/regmap.h>
>  #include <linux/regulator/consumer.h>
> +#include <linux/of_device.h>
>  

Looks like unrelated change...
> -#define MAX31827_T_REG			0x0
> +#define MAX31827_T_REG	0x0
>  #define MAX31827_CONFIGURATION_REG	0x2
> -#define MAX31827_TH_REG			0x4
> -#define MAX31827_TL_REG			0x6
> -#define MAX31827_TH_HYST_REG		0x8
> -#define MAX31827_TL_HYST_REG		0xA
> +#define MAX31827_TH_REG	0x4
> +#define MAX31827_TL_REG 0x6
> +#define MAX31827_TH_HYST_REG	0x8
> +#define MAX31827_TL_HYST_REG	0xA

ditto for all the other places

..

>  
> +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));

sysfs_emit()

> +}
> +
> +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, val2;
> +	int err;
> +
> +	err = kstrtouint(buf, 10, &val);
> +	if (err < 0)
> +		return err;
> +
> +	val2 = FIELD_PREP(MAX31827_CONFIGURATION_PEC_EN_MASK, !!val);
> +

Why not just val?

> +	switch (val) {
> +	case 0:
> +		err = regmap_update_bits(st->regmap, MAX31827_CONFIGURATION_REG,
> +					 MAX31827_CONFIGURATION_PEC_EN_MASK,
> +					 val2);
> +		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,
> +					 val2);
> +		if (err)
> +			return err;
> +
> +		client->flags |= I2C_CLIENT_PEC;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	return count;
> +}
> +static DEVICE_ATTR_RW(pec);
> +
>  static struct attribute *max31827_attrs[] = {
>  	&dev_attr_temp1_resolution.attr,
> +	&dev_attr_pec.attr,

Do we need it in here??


- Nuno Sá