Message-ID: <52546E85.3070407@wwwdotorg.org>
Date:	Tue, 08 Oct 2013 14:43:49 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Nishanth Menon <nm@...com>, Laxman Dewangan <ldewangan@...dia.com>
CC:	"mturquette@...aro.org" <mturquette@...aro.org>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Stephen Warren <swarren@...dia.com>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"broonie@...aro.org" <broonie@...aro.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"rob@...dley.net" <rob@...dley.net>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	J Keerthy <j-keerthy@...com>
Subject: Re: [PATCH V3] clk: palmas: add clock driver for palmas

On 10/08/2013 11:33 AM, Nishanth Menon wrote:
> On 10/08/2013 12:08 PM, Stephen Warren wrote:
>> On 10/08/2013 10:14 AM, Nishanth Menon wrote:
>>> On 10/08/2013 09:39 AM, Laxman Dewangan wrote:
>>>> Thanks Nishanth for review.
>>>>
>>>> On Tuesday 08 October 2013 06:59 PM, Nishanth Menon wrote:
>>>>> On 10/08/2013 08:21 AM, Laxman Dewangan wrote:
>>>>>> Palmas devices has two clock output CLK32K_KG and CLK32K_KG_AUDIO
>>>>> not all palmas devices have 2 clocks - example: tps659038
>>>>
>>>> This is for generic palmas and I have seen it for TPS65913, TPS65914, 
>>>> TPS80036. If the generic one is not compatible then it need to add  
>>>> device specific and at that time, it is require to update the binding 
>>>> document accordingly.
>>>
>>> ?? you do have two clocks inside the device they should be represented
>>> as two compatible entities - that simplifies everyone's life.
>>
>> I think the terminology you're using here is quite confusing.
>>
>> Are you talking about having two different compatible values for two
>> different HW designs, where those different designs implement different
>> sets of clocks (which makes sense), or two different DT nodes for two
>> different clocks (which IMHO doesn't always, unless those different
>> clocks *truly* are separate IP blocks with completely independent
>> register regions, and where those IP blocks are likely to be re-used
>> as-is in other chips).
>
> clk32k and clk32k_audio are two different resources and since these
> are two different resource instances - a "compatible" matching an
> actual device is my suggestion.

The fact that two clocks are two different resources isn't at all
relevant to DT structure. HW module design is what's relevant.

> clk32k and clk32k_audio are two different resources because they have
> their specific set of controls registers and may even be independently
> present in a Palmas variant.

That's a better argument, assuming that: The registers for those two
clocks aren't randomly interleaved with other registers within the HW
module. That would imply that the clock registers aren't independant HW
blocks.

> To highlight this: The example of tps659038 where clk32k is not
> present, but clk32k_audio is present (and happens to be disabled by
> default - thanks to an OTP on the chip - on platform like DRA7-evm, it
> is used to for 32k clk for wlan -currently hacked in u-boot using
> plain i2c writes[1] - yes it is yucky).

That can easily be handled by having separate compatible values for a
monolithic overall Palmas or Palmas-clock node/HW-block. The fact that
different chips are different doesn't, in and of itself, need to
influence whether the different clocks are represented as different DT
nodes.

> Obviously, there are many ways to implement this. based on the current
> implementation, it indicates that if i create a node with
> "ti,palmas-clk" -i'd create two clocks - that is wrong for tps659038.
> 
> Now (with the current approach), if I have to create a one clock for
> tps659038, i have to fix the for adding clock providers, add up
> "ti,tps659038-clk" etc.. it is doable - but IMHO, I dont need to do it
> with only the relevant nodes in dts.
>
> Further, it has no way to indicate that device X uses clock Y using
> clocks =<&xyz> either.

Sorry, I just don't understand that.

If a clock provider provides two clocks, it could number then e.g. 0 and
1. Clock consumers would reference those IDs. If a different chip that
uses the same binding only supports one of those two clocks, just have
the driver return an error if the DT attempts to use/reference the
invalid clock ID; nothign could be simpler.
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