linux-kernel - Re: [rtc-linux] [PATCH 5/6] rtc: max77620: add support for max77620/max20024 RTC driver

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Date:	Mon, 11 Jan 2016 22:37:23 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
CC:	Mark Brown <broonie@...nel.org>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	<rtc-linux@...glegroups.com>, <robh+dt@...nel.org>,
	<pawel.moll@....com>, <mark.rutland@....com>,
	<ijc+devicetree@...lion.org.uk>, <galak@...eaurora.org>,
	<linus.walleij@...aro.org>, <gnurou@...il.com>,
	<lee.jones@...aro.org>, <a.zummo@...ertech.it>,
	<lgirdwood@...il.com>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-gpio@...r.kernel.org>,
	<swarren@...dia.com>, <treding@...dia.com>,
	Chaitanya Bandi <bandik@...dia.com>
Subject: Re: [rtc-linux] [PATCH 5/6] rtc: max77620: add support for max77620/max20024
 RTC driver


On Monday 11 January 2016 09:34 PM, Alexandre Belloni wrote:
> On 11/01/2016 at 18:47:34 +0530, Laxman Dewangan wrote :
>> On Friday 08 January 2016 07:06 PM, Laxman Dewangan wrote:
>>> On Friday 08 January 2016 07:06 PM, Mark Brown wrote:
>>>> * PGP Signed by an unknown key
>>>>
>>>> On Fri, Jan 08, 2016 at 06:34:29PM +0530, Laxman Dewangan wrote:
>>>>
>>>>> If we get the parent device, regmap handle and interrupt number from
>>>>> mfd
>>>>> core independent of the PMIC (MAX77620 or MAX77686), then same driver
>>>>> can be
>>>>> used here.
>>>>> Two way which I can think of here:
>>>> Parent device is just dev->parent, you can use dev_get_regmap() to get a
>>>> regmap given a struct device and you can use platform resources to pass
>>>> the interrupts to the children from the MFD (there's some examples,
>>>> wm831x is one).
>>>>
>>>>
>>> I think it should work with named regmap. mfd whould init regmap with name
>>> and rtc driver should ask with same name.
>>>
>>> I saw three drivers which looks same:
>>> rtc-max77620.c (new from me) and already available rtc-max77686.c,
>>> rtc-max77802.c
>>>
>>> Seems I can develop IP based rtc driver as rtc-max77xxx.c
>> I came with one of issue when doing this.
>>
>> The RTC driver parent is not the same parent for which i2c slave address get
>> registered.
>> There is two slave address from max77620, 0x3C (for general) and 0x68 for
>> RTC.
>>
>> In max77620 mfd driver, we make dummy i2c client for 0x68 and initialize
>> regmap with this address.
>>
>> Now on mfd_add_devices, we pass the device for 0x3c and hence the RTC driver
>> treat the parent as the 0x3c device but actually it should be 0x68 to get
>> the proper regmap.
>>
>>
>> Two approach:
>> 1. If we add the option to pass parent_dev when adding cells form
>> mfd_add_devices and select the parent device based on this option then it
>> can be easily handle.
>>      Add parent_dev structure in struct mfd_cell and then change the parent
>> in mfd_add_device() if cells has parent device.
>>
>> 2. Register the RTC driver with different mfd_add_devices with dummy i2c
>> client device.
>> So two times mfd_add_devices.
>>
>>
>> IMO, approach 1 looks good to me.
>>
>> Any opinion?
>>
> If the RTC is not at the same address, I'd say this is not an mfd
> anymore, can't you probe it directly from DT?
>
>
This approach is also possible but,

although this is independent IP with separate i2c address but became it 
is inside the PMIC and its interrupt depends on PMIC internals, I like 
to register this rtc device from the mfd core.
So that when mfd core is ready with their interrupts and initial 
setting, it can register rtc device.