Re: Duplicated drivers for Epson RX8025 RTC support

[Heiner Kallweit <hkallweit1@gmail.com>]

Am 24.07.2017 um 11:16 schrieb Alexandre Belloni:
> Hi,
> 
> On 23/07/2017 at 22:15:24 +0200, Heiner Kallweit wrote:
>> When working on refactoring parts of the ds1307 I stumbled across the fact
>> that there are two rtc drivers claiming to support the Epson RX8025 chip.
>>
>> 1. ds1307 claims to support also this chip. Support was added in 2009,
>>    however I have doubts that it actually works.
>>    RX8025 needs a special addressing mode (register address has to be
>>    left-shifted by 4 bits) which is implemented for both control
>>    registers but not for the standard registers.
>>
After checking again it could work due to the fact that mainly bulk ops
starting with address 0 are used. Therefore the missing shift doesn't hurt.

>>    Also support for this chip misses the fix from patch 2e10e74df72
>>    ("rtc: rx8025: fix transfer mode")
>>
>>    I'm curious whether support for this chip was ever tested, commit message
>>    of a216685818a5 "rtc: add EPSON RX8025 support to DS1307 RTC driver"
>>    does not mention that this piece of code was tested with any device
>>    with this chip.
>>
>> 2. There's a separate driver for this chip (rtc-rx8025), also added in 2009.
>>    This drivers is actively maintained.
>>
>> The separate driver mentions that it supports SA/NB variants of the chip.
>> There's no info regarding supported chip variants in the ds1307-integrated
>> driver. So there is a small chance that both drivers support different
>> chip variants (in this case however the ds1307-integrated driver should
>> clearly mention this, also in the Kconfig help text).
>>
>> For me it's more likely that both drivers try support the same chip.
>> Having said that I would propose to remove (rudimentary) RX8025 support
>> in ds1307. As a first step we could leave the code in but use a WARN_ON
>> to notify potential users that this code is deprecated and they should
>> use the separate driver instead.
>>
> 
> The remaining issue is described here:
> https://groups.google.com/d/msg/rtc-linux/M_uv9YkRbC8/MaKpMa3LGgAJ
> 
Thanks a lot for sharing the link. So I involve the people from the
previous discussion.

> It is even more apparent after your regmap rework.
> 
Most likely best would be to switch rtc-rx8025 to regmap-i2c as well
as it automatically selects proper low-level access methods based on
the supported i2c functions.
Shouldn't be a big deal using 11e5890b5342 "rtc: ds1307: convert driver
to regmap" as blueprint.

Afterwards support for rx8025 in ds1307 could be dropped.

Rgds, Heiner