linux-kernel - Re: [PATCH 2/2] hwmon: (pmbus): Add driver for BluTek BPA-RS600

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Message-ID: <dff0a92c-a888-2b96-a51c-c5efb3e977af@roeck-us.net>
Date:   Mon, 15 Mar 2021 21:50:27 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "jdelvare@...e.com" <jdelvare@...e.com>
Cc:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] hwmon: (pmbus): Add driver for BluTek BPA-RS600

On 3/15/21 9:21 PM, Chris Packham wrote:
> 
> On 16/03/21 4:43 pm, Guenter Roeck wrote:
>> On 3/15/21 7:35 PM, Chris Packham wrote:
>>> The BPA-RS600 is a compact 600W AC to DC removable power supply module.
>>>
>>> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
>>> ---
> <snip>
>>> +
>>> +static int bpa_rs600_read_word_data(struct i2c_client *client, int page,
>>> +		int phase, int reg)+{
>>> +	int ret;
>>> +
>>> +	if (page > 0)
>>> +		return -ENXIO;
>>> +
>>> +	switch (reg) {
>>> +	case PMBUS_VIN_UV_FAULT_LIMIT:
>>> +	case PMBUS_VIN_OV_FAULT_LIMIT:
>>> +	case PMBUS_VOUT_UV_FAULT_LIMIT:
>>> +	case PMBUS_VOUT_OV_FAULT_LIMIT:
>>> +		ret = -ENXIO;
>> Is that needed ? Why not -ENODATA ?
> 
> Basically these commands get responses on the bus but they don't have 
> valid data (nor are they documented in the datasheet). I'll add a 
> comment to that effect.
> 
> If I'm reading things correctly -ENODATA is a signal to 
> _pmbus_read_word_data use the "normal" read operation. So I need to 

Correct.

> return something other than that. I found another driver (mp2975.c) 
> doing the same thing for what I assume are similar reasons so I went 
> with -ENXIO.
> 
-ENXIO is ok, but please document it.

Thanks,
Guenter