linux-kernel - Re: [PATCH v7 1/6] dt-bindings: ti-lmu: Remove LM3697

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Message-ID: <be2ee681-7ae0-6545-0208-6ae5c1b7affd@gmail.com>
Date:   Sat, 15 Sep 2018 22:00:37 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Dan Murphy <dmurphy@...com>, robh+dt@...nel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        lee.jones@...aro.org, linux-omap@...r.kernel.org,
        linux-leds@...r.kernel.org
Subject: Re: [PATCH v7 1/6] dt-bindings: ti-lmu: Remove LM3697

Hi Pavel.

On 09/14/2018 11:42 PM, Pavel Machek wrote:
> Hi!
> 
>>> You may want to learn more about device tree and/or talk to the device
>>> tree maintainers. This is an old article. https://lwn.net/Articles/561462/
>>
>> The article title is "Device trees as ABI". A device tree is defined
>> in the "*.dts" file that is then compiled to a dtb blob, which
>> constitutes the ABI. And this ABI should be kept backwards compatible.
>>
>> What is discussed here is a documentation of bindings, i.e. according
>> to ePAPR: "requirements for how specific types and classes of devices
>> are represented in the device tree".
>>
>> >From the bindings documented in the
>> Documentation/devicetree/bindings/mfd/ti-lmu.txt only
>> ti,lm3532-backlight is used in the mainline dts file
>> (arch/arm/boot/dts/omap4-droid4-xt894.dts).
>>
>> Having the above it seems that there is no risk of breaking any
>> users.
> 
> DTBs and bindings are supposed to be portable between operating
> systems. You are right there are no _mainline_ _Linux_ users.

No mainline users means no users we should care of.
Other people also don't care - see patch [0].

>>> NAK on this patch. I see that this binding has problems, but
>>> introducing different binding for subset of devices is _not_ a fix.
>>>
>>>>> What about the multi function devices? They should have same binding.
>>>>
>>>> The MFD devices defined are not in contention here only the SFD.
>>>
>>> I'd like to see common solutions for SFD and MFD, as the hardware is
>>> similar, and that includes the code. Having code that is easier to
>>> maintain is important, and having many drivers are harder to maintain
>>> than one driver.
>>>
>>> Milo's code looks better than yours in that regard. I disagree about
>>> Milo's code being "nightmare" to modify, and care about "easy to
>>> maintain" more than "binary size".
>>
>> Easy to maintain will be a dedicated LED class driver.
> 
> You mean, 3 dedicated LED class drivers and 3 MFD drivers with LED
> parts? We'll need complex driver anyway, and I'd really like to have
> just one.

In the LED subsystem we can wrap common functionalities
into a library object. MFD driver will be able to reuse it then.

[0]
https://git.kernel.org/pub/scm/linux/kernel/git/tmlind/linux-omap.git/commit/?h=droid4-pending-v4.19&id=d774c7e447ac911e73a1b3c775e6d89f0422218c

-- 
Best regards,
Jacek Anaszewski