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

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Date: Fri, 24 May 2024 09:00:13 +0200
From: Nuno Sá <noname.nuno@...il.com>
To: Guenter Roeck <linux@...ck-us.net>, 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 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()...

- Nuno Sá