linux-kernel - Re: [PATCH v2 0/4] Add support for Exynos clock output configuration

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Date:	Wed, 25 Jun 2014 12:50:42 +0200
From:	Tomasz Figa <t.figa@...sung.com>
To:	Kukjin Kim <kgene.kim@...sung.com>,
	linux-samsung-soc@...r.kernel.org
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	'Marek Szyprowski' <m.szyprowski@...sung.com>,
	'Mike Turquette' <mturquette@...aro.org>,
	'Rob Herring' <robh+dt@...nel.org>,
	'Mark Rutland' <mark.rutland@....com>,
	'Pankaj Dubey' <pankaj.dubey@...sung.com>,
	'Rahul Sharma' <rahul.sharma@...sung.com>,
	'Mark Brown' <broonie@...nel.org>,
	'Sylwester Nawrocki' <s.nawrocki@...sung.com>,
	'Daniel Drake' <drake@...lessm.com>,
	'Tomasz Figa' <tomasz.figa@...il.com>
Subject: Re: [PATCH v2 0/4] Add support for Exynos clock output configuration

Hi Kukjin,

On 25.06.2014 12:36, Kukjin Kim wrote:
> Tomasz Figa wrote:
>>
> Hi Tomasz,
> 
>> On all Exynos SoCs there is a dedicated CLKOUT pin that allows many of
>> internal SoC clocks to be output from the SoC. The hardware structure
> 
> Yeah, because the CLKOUT pin is used for measure of the clock for debug on all
> of exynos SoCs commonly.
> 
>> of CLKOUT related clocks looks as follows:
>>
>> 	CMU	|---> clock0 --------->	|	PMU	|
>> 		|			|		|
>>     several	|---> clock1 ---------> |	mux	|
>>     muxes	|			|	+	|---> CLKOUT
>>     dividers	|       ...		|	gate	|
>>     and gates	|			|		|
>> 		|---> clockN ---------> |		|
>>
>> Since the block responsible for handling the pin is PMU, not CMU,
>> a separate driver, that binds to PMU node is required and acquires
>> all input clocks by standard DT clock look-up. This way we don't need
>> any cross-IP block drivers and cross-driver register sharing or
>> nodes for fake devices.
>>
> BTW, upcoming exynos5 SoCs have two muxs for CLKOUT and each mux is controlled
> by CMU and PMU, so
> 
> The mux1 for CLKOUT in CMU is used to decide which clock in each sub-domain
> will be out and the mux2 in PMU is used to decide which sub-domain will be out
> via CLKOUT. So I want you to consider of all of exynos SoCs including upcoming
> SoCs.

Is it something similar to what I implemented for Exynos4 in patch 2/4?
The same has to be done for other Exynos SoCs as well, but i don't have
any board on which I could test this, so I just added a subset of
available inputs of PMU mux in current implementation.

Anyway, anything in CMU can be handled in normal SoC clock driver, so I
don't think this poses any problem for this series.

Best regards,
Tomasz
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