linux-kernel - Re: [PATCH 4/4] mfd: tps65217: Instantiate sub-devices from device tree

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Message-ID: <CABxcv=nzCreCSm9wkY+Kv_-vmoQN12Ct=_VegsfTrbe6H-1hTw@mail.gmail.com>
Date:   Fri, 9 Jun 2017 02:00:01 +0200
From:   Javier Martinez Canillas <javier@...hile0.org>
To:     Grygorii Strashko <grygorii.strashko@...com>
Cc:     Enric Balletbo Serra <eballetbo@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Tony Lindgren <tony@...mide.com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-leds@...r.kernel.org, linux-input@...r.kernel.org,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH 4/4] mfd: tps65217: Instantiate sub-devices from device tree

Hello Grygorii,

[snip]

>>
>> For tps65218 couldn't instead of using mfd_add_devices() for all the
>> sub-devs, had used of_platform_populate() for the ones that have
>> device nodes and mfd_add_devices() only for the "tps65218-regulator"?
>>
>> The commit talks about nodes without compatibles but's actually about
>> sub-devices without an associated device node. For me it makes sense
>> to use of_platform_populate() when the MFD has device nodes for their
>> sub-devices and mfd_add_devices() when DT knows nothing about the
>> sub-devices.
>
> FYI. Below is link discussion I'm referring to between Mark Brown and Andrew F. Davis
> https://lkml.org/lkml/2015/10/22/823
> the same - https://groups.google.com/forum/#!topic/linux.kernel/wQsdSpPMroQ
>

Thanks a lot for the pointer. There's a subtle difference between the
argument you made and the one that Mark is making in this thread
though.

Because you said (sorry if I misunderstood) that mfd_add_devices()
should be used instead of of_device_populate() even when sub-devices
are described as DT nodes (as is the case in the commit you shared)
while Mark is saying that if the sub-devs IP blocks are part of the
MFD, then it shouldn't be exposed in the DT and be instantiated via
mfd_add_devices() and I absolutely agree with that.

So I was arguing for using of_device_populate() if the sub-devices are
described in the DT. If that makes sense or not to expose the
sub-devices in the DT for this particular driver is a different
discussion and I can't comment on that since I'm not familiar with the
HW.

Best regards,
Javier