linux-kernel - Re: [PATCH] mfd: max77686: make interrupts support optional

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Message-ID: <53F45C73.1030304@collabora.co.uk>
Date:	Wed, 20 Aug 2014 10:29:39 +0200
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Lee Jones <lee.jones@...aro.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Daniel Drake <drake@...lessm.com>,
	Tobias Jakobi <Liquid.Acid@....net>,
	Olof Johansson <olof@...om.net>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Subject: Re: [PATCH] mfd: max77686: make interrupts support optional

Hello Lee, Marek,

On 08/20/2014 10:19 AM, Lee Jones wrote:
> On Wed, 20 Aug 2014, Marek Szyprowski wrote:
> 
>> Commit 6f1c1e71d93 ("mfd: max77686: Convert to use regmap_irq") broke
>> support for boards, which provide no irq for MAX 77686 PMIC. In such
>> case, not all functions of PMIC are available, but the driver still
>> should at least handle voltage regulators instead of failing to init.
>> This patch restores previous behavior.
>> 
>> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
>> ---
>> Hello,
>> 
>> This patch fixes booting issues with recently merged support for
>> Exynos4412 based Odroid X2/U3 boards. See
>> http://www.spinics.net/lists/linux-samsung-soc/msg35773.html
>> thread for more details.
>> 
>> Best regards
>> Marek Szyprowski
>> Samsung R&D Institute Poland

I already gave my opinion about this patch on thread:

"[PATCH v2 0/4] Add Exynos4412 based Odroid X2 and U2/U3/U3+ support"

where the issue was reported by Olof but I'll add it here as well for
completeness since I don't know if the same people are cc'ed on both threads.

Bartlomiej Zolnierkiewicz posted a similar patch [0] before but as I said
on that thread, I'm not sure if is correct to make that DT property
optional. Or rather, if we need to make it optional then we should also
change the Documentation/devicetree/bindings/mfd/max77686.txt that list
"interrupts" DT property as required.

It's true that before converting the max77686 to use the regmap irq API,
the driver was loose on that regard but max77686_irq_init() in
max77686-irq.c was returning -ENODEV when the IRQ was not provided and
that error code was not checked in max77686_i2c_probe() (which was a bug
IMHO).

More importantly I wonder if a design where a IRQ line is not connected to
the max77686 PMIC makes even sense. If such a design is possible then the
"interrupt" property should be made optional but if not then I think that
the driver should fail to probe in that case. Yes, it is a regression but
the Odroid DTS was not following the DT binding and was just lucky that
the driver was not checking the required DT properties.

Daniel Drake posted the correct fix for the Odroid DTS [1]. So I tend to
say that Daniel's fix should be added as a -rc fix and we should keep both
the max77686 driver and its DT binding as it is now but as I said, if from
a hardware point of view makes sense to leave that line unconnected then I
don't oppose to this change.

Best regards,
Javier

[0]: https://lkml.org/lkml/2014/8/7/374
[1]:
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-July/272869.html
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