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

From: Laxman Dewangan
Date: Mon Jan 11 2016 - 12:17:45 EST

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
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,

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
There is two slave address from max77620, 0x3C (for general) and 0x68 for

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.