linux-kernel - Re: [PATCH 2/2] hwmon: pmbus: adm1275: add adm1281 support

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Message-ID: <62f878f4-a4fb-4e3c-8eec-d1be5ba165a4@roeck-us.net>
Date: Wed, 17 Apr 2024 08:24:59 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Jose Ramon San Buenaventura <jose.sanbuenaventura@...log.com>
Cc: linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-i2c@...r.kernel.org, Jean Delvare <jdelvare@...e.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Delphine CC Chiu <Delphine_CC_Chiu@...ynn.com>
Subject: Re: [PATCH 2/2] hwmon: pmbus: adm1275: add adm1281 support

On Tue, Apr 16, 2024 at 05:32:46PM -0700, Guenter Roeck wrote:
> On Wed, Apr 17, 2024 at 08:07:22AM +0800, Jose Ramon San Buenaventura wrote:
> > Adding support for adm1281 which is similar to adm1275
> > 
> > ADM1281 has STATUS_CML read support which is also being added.
> > 
> > Signed-off-by: Jose Ramon San Buenaventura <jose.sanbuenaventura@...log.com>
> > ---
> >  Documentation/hwmon/adm1275.rst | 14 +++++++++++---
> >  drivers/hwmon/pmbus/Kconfig     |  4 ++--
> >  drivers/hwmon/pmbus/adm1275.c   | 27 +++++++++++++++++++++++++--
> >  3 files changed, 38 insertions(+), 7 deletions(-)
> > 
> > diff --git a/Documentation/hwmon/adm1275.rst b/Documentation/hwmon/adm1275.rst
> > index 804590eea..467daf8ce 100644
> > --- a/Documentation/hwmon/adm1275.rst
> > +++ b/Documentation/hwmon/adm1275.rst
> > @@ -43,6 +43,14 @@ Supported chips:
> >  
> >      Datasheet: www.analog.com/static/imported-files/data_sheets/ADM1278.pdf
> >  
> > +  * Analog Devices ADM1281
> > +
> > +    Prefix: 'adm1281'
> > +
> > +    Addresses scanned: -
> > +
> > +    Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/adm1281.pdf
> > +
> >    * Analog Devices ADM1293/ADM1294
> >  
> >      Prefix: 'adm1293', 'adm1294'
> > @@ -58,10 +66,10 @@ Description
> >  -----------
> >  
> >  This driver supports hardware monitoring for Analog Devices ADM1075, ADM1272,
> > -ADM1275, ADM1276, ADM1278, ADM1293, and ADM1294 Hot-Swap Controller and
> > +ADM1275, ADM1276, ADM1278, ADM1281, ADM1293, and ADM1294 Hot-Swap Controller and
> >  Digital Power Monitors.
> >  
> > -ADM1075, ADM1272, ADM1275, ADM1276, ADM1278, ADM1293, and ADM1294 are hot-swap
> > +ADM1075, ADM1272, ADM1275, ADM1276, ADM1278, ADM1281, ADM1293, and ADM1294 are hot-swap
> >  controllers that allow a circuit board to be removed from or inserted into
> >  a live backplane. They also feature current and voltage readback via an
> >  integrated 12 bit analog-to-digital converter (ADC), accessed using a
> > @@ -144,5 +152,5 @@ temp1_highest		Highest observed temperature.
> >  temp1_reset_history	Write any value to reset history.
> >  
> >  			Temperature attributes are supported on ADM1272 and
> > -			ADM1278.
> > +			ADM1278, and ADM1281.
> >  ======================= =======================================================
> > diff --git a/drivers/hwmon/pmbus/Kconfig b/drivers/hwmon/pmbus/Kconfig
> > index 557ae0c41..9c1d0d7d5 100644
> > --- a/drivers/hwmon/pmbus/Kconfig
> > +++ b/drivers/hwmon/pmbus/Kconfig
> > @@ -51,8 +51,8 @@ config SENSORS_ADM1275
> >  	tristate "Analog Devices ADM1275 and compatibles"
> >  	help
> >  	  If you say yes here you get hardware monitoring support for Analog
> > -	  Devices ADM1075, ADM1272, ADM1275, ADM1276, ADM1278, ADM1293,
> > -	  and ADM1294 Hot-Swap Controller and Digital Power Monitors.
> > +	  Devices ADM1075, ADM1272, ADM1275, ADM1276, ADM1278, ADM1281,
> > +	  ADM1293, and ADM1294 Hot-Swap Controller and Digital Power Monitors.
> >  
> >  	  This driver can also be built as a module. If so, the module will
> >  	  be called adm1275.
> > diff --git a/drivers/hwmon/pmbus/adm1275.c b/drivers/hwmon/pmbus/adm1275.c
> > index e2c61d6fa..6c3e8840f 100644
> > --- a/drivers/hwmon/pmbus/adm1275.c
> > +++ b/drivers/hwmon/pmbus/adm1275.c
> > @@ -18,7 +18,7 @@
> >  #include <linux/log2.h>
> >  #include "pmbus.h"
> >  
> > -enum chips { adm1075, adm1272, adm1275, adm1276, adm1278, adm1293, adm1294 };
> > +enum chips { adm1075, adm1272, adm1275, adm1276, adm1278, adm1281, adm1293, adm1294 };
> >  
> >  #define ADM1275_MFR_STATUS_IOUT_WARN2	BIT(0)
> >  #define ADM1293_MFR_STATUS_VAUX_UV_WARN	BIT(5)
> > @@ -101,6 +101,7 @@ struct adm1275_data {
> >  	bool have_pin_max;
> >  	bool have_temp_max;
> >  	bool have_power_sampling;
> > +	bool have_status_cml;
> >  	struct pmbus_driver_info info;
> >  };
> >  
> > @@ -469,6 +470,22 @@ static int adm1275_read_byte_data(struct i2c_client *client, int page, int reg)
> >  				ret |= PB_VOLTAGE_UV_WARNING;
> >  		}
> >  		break;
> > +	case PMBUS_STATUS_CML:
> > +		if (!data->have_status_cml)
> > +			return -ENXIO;
> > +
> > +		ret = pmbus_read_byte_data(client, page, PMBUS_STATUS_BYTE);
> > +		if (ret < 0)
> > +			break;
> 
> You'll have to explain why this additional status byte read
> is necessary (while it isn't necessary for all other chips supporting
> PMBUS_STATUS_CML).
> 

After looking more into the existing PMBus code and into this patch,
I really fail to understand why the above change would be needed.
The PMBus core code already reads the status register to check if
there is a communication error. I fail to see why it would be necessary
to do it again, and why it would be necessary to change behavior for
the other chips supported by this driver.

Guenter