Re: ABI for these two registers?

From: Guenter Roeck <linux@roeck-us.net>
To: Nicolin Chen <nicoleotsuka@gmail.com>
Cc: linux-hwmon@vger.kernel.org
Subject: Re: ABI for these two registers?
Date: Wed, 2 Oct 2019 22:03:11 -0700	[thread overview]
Message-ID: <a863488c-29fa-394c-3e3a-2761d18a0052@roeck-us.net> (raw)
In-Reply-To: <20191001221735.GA27958@Asurada-Nvidia.nvidia.com>

On 10/1/19 3:17 PM, Nicolin Chen wrote:
> Hello Guenter,
> 
> It's been nearly three weeks. Would it be possible for you to
> provide some advice on my latest questions? I'd like to write
> code and submit changes once ABI is confirmed...
> 

Non-standard attribute discussions always require a lot of time,
since I have to re-read the chip documentation and try to understand
the reasoning why the attributes are needed. On top of that,
asking me "what should I do" instead of suggesting possible
solutions for me to choose from takes even more time, which
unfortunately I don't have right now. I'll try to get to it,
but, sorry, I can not promise you a time right now.

Guenter

> Thank you!
> 
> On Thu, Sep 12, 2019 at 05:12:38PM -0700, Nicolin Chen wrote:
> 
>>>>>>> Datasheet: http://www.ti.com/lit/ds/symlink/ina3221.pdf
>>>>>>> (At page 32, chapter 8.6.2.14 and 8.6.2.15)
>>>>>>>
>>>>>>> I have two registers that I need to expose to user space:
>>>>>>> 	Shunt-Voltage-Sum and Shunt-Voltage-Limit registers
>>>>>>>
>>>>>>> Right now in[123]_input of INA3221 are for voltage channels
>>>>>>> while in[456]_input are for Shunt voltage channels.
>>>>>>>
>>>>>>> So can I just use in7_input and in7_crit for them?
>>>>>>>
>>>>>> Doesn't Shunt-Voltage-Limit apply to in[456]_input ?
>>>>>> If so, the limit should be attached to those.
>>>>>
>>>>> The initial patch of ina3221 driver applied Shunt-Voltage-Limits,
>>>>> being named as "Critical Alert Limit Registers" in the datasheet,
>>>>> to curr[123]_crit, corresponding to curr[123] and in[456]_input.
>>>>>
>>>>> And this Shunt-Voltage-Limit-Sum is more related to the reading
>>>>> from Shunt-Voltage-Sum, which we just agreed it to be in7_input.
>>>>>
>>>> You didn't say Shunt-Voltage-Limit-Sum earlier. You said
>>>
>>> Ah....right...it's my fault. Sorry.
>>>
>>>> Shunt-Voltage-Limit. I would agree that Shunt-Voltage-Limit-Sum is
>>>> associated with Shunt-Voltage-Sum, but, again, that is not what you
>>>> said earlier. Confused :-(
>>>
>>> So, those two should be in7_input and in7_crit?
>>
>> And a couple of more questions upon it:
>>
>> 1) There are 3 control bits for the summation of this
>>     shunt-voltage-sum register to enable corresponding
>>     input channels. But in7_enable only allows users to
>>     en/disable all three channels at the same time. So
>>     how should I attach three enable bits using ABI?
>>     Or should I create a device-specific sysfs node?
>>
>> 2) We have a requirement of providing current-sum and
>>     current-limit-sum nodes, for use cases where those
>>     enabled channels use same value shunt resistors.
>>     It's similar to provide curr[1-3]_crit by dividing
>>     shunt[123]_resistor from in[456]_input. So could I
>>     deploy curr4_input and curr4_crit nodes for this
>>     requirement?
> 