linux-kernel - Re: [PATCHv1] rtc: bcm-iproc: Add support for Broadcom iproc rtc

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Date:	Wed, 11 Mar 2015 13:00:22 -0700
From:	Arun Ramamurthy <arun.ramamurthy@...adcom.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Ray Jui <rjui@...adcom.com>,
	<linux-arm-kernel@...ts.infradead.org>, <mark.rutland@....com>,
	<a.zummo@...ertech.it>, <sbranden@...adcom.com>,
	<pawel.moll@....com>, <devicetree@...r.kernel.org>,
	<ijc+devicetree@...lion.org.uk>,
	Arun Ramamurthy <arunrama@...adcom.com>,
	<linux-kernel@...r.kernel.org>, <grant.likely@...aro.org>,
	<robh+dt@...nel.org>, <bcm-kernel-feedback-list@...adcom.com>,
	<galak@...eaurora.org>, <rtc-linux@...glegroups.com>
Subject: Re: [PATCHv1] rtc: bcm-iproc: Add support for Broadcom iproc rtc



On 15-03-04 02:58 PM, Arnd Bergmann wrote:
> On Wednesday 04 March 2015 14:53:40 Arun Ramamurthy wrote:
>> On 15-03-04 02:50 PM, Arnd Bergmann wrote:
>>> On Wednesday 04 March 2015 14:40:13 Arun Ramamurthy wrote:
>>>> On 15-03-04 02:21 PM, Arnd Bergmann wrote:
>>>>> On Thursday 12 February 2015 14:17:41 Arun Ramamurthy wrote:
>>>>>> Hi Arnd
>>>>>>
>>>>>> My apologies for the late reply, I was moved to other work items. I
>>>>>> wanted to get more clarification on the syscon issue so that I can
>>>>>> submit the next patch set. If I understand correctly, you would like
>>>>>> me to move the CRMU logic to a new driver under mfd/ and use the syscon
>>>>>> api calls in my rtc driver? Thanks
>>>>>
>>>>> It depends a lot on what's in there, I can best advise you if you
>>>>> have some form of register list.
>>>>>
>>>>> A common approach would be to not have a driver for the crmu at all,
>>>>> but just mark it as syscon, and have the other drivers either reference
>>>>> the syscon node through a phandle, or create them as childrem of
>>>>> the syscon node. The latter case makes most sense if all uses of
>>>>> the crmu have no other MMIO registers.
>>>>>
>>>>
>>>> Thank you Arnd, I am going to follow the approach of adding a child node
>>>> to the syscon node. Several other driver use other registers in the CRMU
>>>> so I think the child node approach makes the most sense.
>>>
>>> Just to be sure we have the same understanding: of those other drivers,
>>> do you think that they would use only CRMU registers, or could there
>>> be drivers that have both CRMU as well as other MMIO registers?
>>>
>> The other drivers have both CRMU and other MMIO registers. So I thought
>> they could also switch to using the syscon child nodes.
>>
>
> No, in this case, better not use child nodes at all. When other platforms
> use child nodes of a syscon, the common case is that they use the 'reg'
> property to refer to syscon registers, which are in a different address
> space from other MMIO, and you can't easily mix the two.
>

Arnd, this is the device tree entry that I would end up with and I plan 
to use syscon_regmap_lookup_by_phandle in the rtc driver. Does this look 
acceptable?

rtc: iproc_rtc@...3026000 {
		compatible = "brcm,iproc-rtc";
		reg =	<0x03026000 0xC>,
		iso_cell_syscon = <&crmu_iso_cell_control>;
		bbl_auth_syscon = <&crmu_bbl_auth>
		status = "okay";

crmu_iso_cell_control:crmu@...301C02C {
		compatible = "syscon";
		reg = <0x0301C038 0x8>
}

crmu_bbl_auth:crmu@...3024C74 {
		compatible = "syscon";
		reg = <0x03024C74 0x8>;
}

Thanks
> 	Arnd
>
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