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 17:04:19 +0100
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Laxman Dewangan <ldewangan@...dia.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 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?


-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com