linux-kernel - Re: [PATCH v4 07/14] mfd: Add driver for Maxim 77802 Power Management IC

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Date:	Thu, 26 Jun 2014 09:29:51 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
Cc:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Lee Jones <lee.jones@...aro.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Mark Brown <broonie@...nel.org>,
	Mike Turquette <mturquette@...aro.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Olof Johansson <olof@...om.net>,
	Sjoerd Simons <sjoerd.simons@...labora.co.uk>,
	Daniel Stone <daniels@...labora.com>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 07/14] mfd: Add driver for Maxim 77802 Power Management IC

Javier,

On Thu, Jun 26, 2014 at 9:18 AM, Javier Martinez Canillas
<javier.martinez@...labora.co.uk> wrote:
> Hello Doug,
>
> On 06/26/2014 06:12 PM, Doug Anderson wrote:
>> Javier,
>>
>> On Thu, Jun 26, 2014 at 4:13 AM, Javier Martinez Canillas
>> <javier.martinez@...labora.co.uk> wrote:
>>>>> +
>>>>> +#ifdef CONFIG_PM_SLEEP
>>>>> +static int max77802_suspend(struct device *dev)
>>>>> +{
>>>>> +    struct i2c_client *i2c = container_of(dev, struct i2c_client, dev);
>>>>> +    struct max77802_dev *max77802 = i2c_get_clientdata(i2c);
>>>>> +
>>>>> +    if (device_may_wakeup(dev))
>>>>> +            enable_irq_wake(max77802->irq);
>>>>> +
>>>>> +    disable_irq(max77802->irq);
>>>>
>>>> Can you add short comment why this is needed? I know why but just for
>>>> future generations which will wonder: "why do we need to disable the IRQ
>>>> while suspending?" :). Especially that this is rather a workaround for
>>>> issue in other driver (I2C bus).
>>>>
>>>
>>> Good idea, I'll add a comment here on next version so code archaeologists can
>>> figure out what what's going on here.
>>
>> Is the disable_irq() needed if you have
>> <https://patchwork.kernel.org/patch/4421891/>?
>>
>
> Probably not but I added the following comment:
>
>         /*
>          * The IRQ must be disabled during suspend since due wakeup
>          * ordering issues it may be possible that the I2C controller
>          * is still suspended when the interrupt happens so the IRQ
>          * handler will fail to read the I2C bus.
>          */
>         disable_irq(max77802->irq);
>
> since in theory this PMIC can be used in other SoCs besides
> Exynos5420/Exynos5800 and it may be possible that the I2C controller driver for
> these other SoCs may not resume at noirq time.
>
> But on a second thought, this PMIC seems to be designed specially for these two
> Exynos SoCs so I guess it's safe to assume that it is not needed?

Right, there's a close coupling between PMICs and SoCs.  The PMIC has
special sequencing and default voltage levels that were tuned exactly
for this SoC.

Note: Wolfram has not actually responded to my patch much less
accepted it.  It's entirely possible that in another month or two
we'll hear back a big fat NAK.  In that case your solution will be the
best one I can think of.


-Doug
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