linux-kernel - Re: [PATCH V3] clk: palmas: add clock driver for palmas

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Message-ID: <525441DD.2090109@ti.com>
Date:	Tue, 8 Oct 2013 12:33:17 -0500
From:	Nishanth Menon <nm@...com>
To:	Stephen Warren <swarren@...dotorg.org>,
	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 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.

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.

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).

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.

[1] DRA7-evm u-boot hack.
i2c dev 0
i2c probe
i2c mw 0x58 0xfb 0x2b (select secondary function for GPIO_5)
i2c mw 0x58 0xd5 0x01 (enable audio clock)

-- 
Regards,
Nishanth Menon
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