linux-kernel - Re: [PATCH v3 2/5] w1_therm: adding sysfs entry to check device power

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Date:   Wed, 29 Apr 2020 18:18:14 +0300
From:   Evgeniy Polyakov <zbr@...emap.net>
To:     Greg KH <greg@...ah.com>, Akira Shimahara <akira215corp@...il.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/5] w1_therm: adding sysfs entry to check device power

Hi

29.04.2020, 16:47, "Greg KH" <greg@...ah.com>:

>>  +What: /sys/bus/w1/devices/.../w1_slave
>>  +Date: Apr 2020
>>  +Contact: Akira Shimahara <akira215corp@...il.com>
>>  +Description:
>>  + (RW) return the temperature in 1/1000 degC.
>>  + *read*: return 2 lines with the hexa output data sent on the
>>  + bus, return the CRC check and temperature in 1/1000 degC
>
> the w1_slave file returns a temperature???
>
> And sysfs is 1 value-per-file, not multiple lines.

It was 'content crc' previously, and probably a good idea would be to add just one file with 'content'

> And as this is a temperature, what's wrong with the iio interface that
> handles temperature already? Don't go making up new userspace apis when
> we already have good ones today :)

What is that?
w1 always had a sysfs files for its contents whether it is converted temperature or raw bytes data,
there is also netlink interface which is there since the day one. 

>>  + *write* :
>>  + * `0` : save the 2 or 3 bytes to the device EEPROM
>>  + (i.e. TH, TL and config register)
>>  + * `9..12` : set the device resolution in RAM
>>  + (if supported)
>
> I don't understand these write values, how do they match up to a
> temperature readin?

You kind of writing to device about how to convert its raw content into readable content, which will eventually become a temperature