Message-ID: <9a6ba152-3d17-3f9c-782c-1f10aa74691b@topic.nl>
Date:   Thu, 29 Jun 2017 09:45:32 +0200
From:   Mike Looijmans <mike.looijmans@...ic.nl>
To:     Tom Levens <tom.levens@...n.ch>, Guenter Roeck <linux@...ck-us.net>
CC:     <jdelvare@...e.com>, <robh+dt@...nel.org>, <mark.rutland@....com>,
        <linux-kernel@...r.kernel.org>, <linux-hwmon@...r.kernel.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] hwmon: ltc2990: support all measurement modes

On 28-06-17 19:02, Tom Levens wrote:
> 
> On Wed, 28 Jun 2017, Guenter Roeck wrote:
> 
>> On Wed, Jun 28, 2017 at 05:29:38PM +0200, Tom Levens wrote:
>>>
>> [ ... ]
>>
>>>>
>>>>> Whatever happened to this patch though? It didn't make it to mainline,
>>>>> otherwise I'd have found it sooner...
>>>>>
>>>> I'll have to look it up, but I guess I didn't get an updated version.
>>>
>>> As far as I remember I had a working V3 of this patch, but it is entirely
>>> possible that it was never submitted as I have been busy with other projects
>>> recently. I'll dig it out and check that it is complete.
>>>
>> FWIW, I don't see it at
>> https://patchwork.kernel.org/project/linux-hwmon/list/?submitter=171225&state=*
>>
>> Maybe you were waiting for a reply from Rob. Either case, it might make
>> sense to only provide valid modes, ie to abstract the mode bits from the
>> hardware, such as
>>
>> 0 - internal temp only
>> 1 - Tr1
>> 2 - V1
>> 3 - V1-V2
>> 4 - Tr2
>> 5 - V3
>> 6 - V3-V4
>> 7 to 14 - per bit 0..2
>>
>> Guenter
>>
> 
> You are right, there was still an open question about how best to handle the 
> mode selection in DT.
> 
> In the latest version of my patch I have it implemented as an array for 
> setting the two values, for example:
> 
>      lltc,meas-mode = <7 3>;
> 
> This sets bits [2..0] = 7 and [4..3] = 3. Of course these could be split into 
> two DT properties, but I was unsure what to name them as both fields are 
> called "mode" in the datasheet and "mode-43"/"mode-20" (or similar) is ugly.
> 
> With regards to your proposal, it is not clear to me whether the modes which 
> have the same result are exactly equivalent. Does disabling a measurement with 
> the mode[4..3] bits really leaves the part in a safe state for all possible HW 
> connections? With this doubt in my head, I would prefer to keep the option 
> available to the user to select any specific mode. But I am open to suggestions.
> 
> Mike, if you would like to test it, the latest version of my code is here:
> 
> https://github.com/levens/ltc2990/blob/dev/drivers/hwmon/ltc2990.c
> 

I pulled your patches, added two lines to the devicetree and it works fine, 
I'm seeing plausible results:
root@...ic-miami:/sys/class/hwmon# grep . */*
hwmon0/name:battery-gauge
hwmon0/temp1_input:291700
hwmon1/in0_input:3258
hwmon1/in1_input:1824
hwmon1/in2_input:1916
hwmon1/in3_input:1512
hwmon1/in4_input:2066
hwmon1/name:ltc2990
hwmon1/temp1_input:28062
hwmon1/uevent:OF_NAME=ltc2990
hwmon1/uevent:OF_FULLNAME=/gpios-i2c@...ltc2990@4c
hwmon1/uevent:OF_COMPATIBLE_0=lltc,ltc2990
hwmon1/uevent:OF_COMPATIBLE_N=1
hwmon2/curr1_input:1825
hwmon2/curr2_input:349
hwmon2/in0_input:3244
hwmon2/name:ltc2990
hwmon2/temp1_input:31500
hwmon2/uevent:OF_NAME=ltc2990
hwmon2/uevent:OF_FULLNAME=/gpios-i2c@...ltc2990@4C
hwmon2/uevent:OF_COMPATIBLE_0=ltc2990
hwmon2/uevent:OF_COMPATIBLE_N=1


As you can see, two ltc2990 on two busses, one measuring current and one 
measuring 4 independent voltages.

I also like your implementation of the mode setting better, it's much simpler 
than mine. And you've solved a bug in the temperature reading as well.



Kind regards,

Mike Looijmans
System Expert

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