linux-kernel - Re: [PATCH v2 14/19] ARM: dts: Add bus nodes using VDD

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Message-id: <56691C70.6080208@samsung.com>
Date:	Thu, 10 Dec 2015 15:32:16 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Chanwoo Choi <cw00.choi@...sung.com>, myungjoo.ham@...sung.com,
	kgene@...nel.org
Cc:	kyungmin.park@...sung.com, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, linux@....linux.org.uk,
	tjakobi@...h.uni-bielefeld.de, linux.amoon@...il.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 14/19] ARM: dts: Add bus nodes using VDD_INT for
 Exynos4x12

On 10.12.2015 15:08, Chanwoo Choi wrote:
> On 2015년 12월 10일 14:57, Krzysztof Kozlowski wrote:
>> On 09.12.2015 13:08, Chanwoo Choi wrote:
>>> This patch adds the bus noes using VDD_INT for Exynos4x12 SoC.
>>> Exynos4x12 has the following AXI buses to translate data between
>>> DRAM and sub-blocks.
>>>
>>> Following list specifies the detailed relation between DRAM and sub-blocks:
>>> - ACLK100 clock for PERIL/PERIR/MFC(PCLK)
>>> - ACLK160 clock for CAM/TV/LCD
>>> : The minimum clock of ACLK160 should be over 160MHz.
>>>   When drop the clock under 160MHz, show the broken image.
>>> - ACLK133 clock for FSYS
>>> - GDL clock for LEFTBUS
>>> - GDR clock for RIGHTBUS
>>> - SCLK_MFC clock for MFC
>>>
>>> Signed-off-by: Chanwoo Choi <cw00.choi@...sung.com>
>>> ---
>>>  arch/arm/boot/dts/exynos4x12.dtsi | 112 ++++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 112 insertions(+)
>>>
>>> diff --git a/arch/arm/boot/dts/exynos4x12.dtsi b/arch/arm/boot/dts/exynos4x12.dtsi
>>> index 3bcf0939755e..8bc4aee156b5 100644
>>> --- a/arch/arm/boot/dts/exynos4x12.dtsi
>>> +++ b/arch/arm/boot/dts/exynos4x12.dtsi
>>> @@ -354,6 +354,118 @@
>>>  			opp-microvolt = <950000>;
>>>  		};
>>>  	};
>>> +
>>> +	bus_leftbus: bus_leftbus {
>>> +		compatible = "samsung,exynos-bus";
>>> +		clocks = <&clock CLK_DIV_GDL>;
>>> +		clock-names = "bus";
>>> +		operating-points-v2 = <&bus_leftbus_opp_table>;
>>> +		status = "disabled";
>>> +	};
>>> +
>>> +	bus_rightbus: bus_rightbus {
>>> +		compatible = "samsung,exynos-bus";
>>> +		clocks = <&clock CLK_DIV_GDR>;
>>> +		clock-names = "bus";
>>> +		operating-points-v2 = <&bus_leftbus_opp_table>;
>>> +		status = "disabled";
>>> +	};
>>
>> These two nodes are symmetrical. The MFC below and other buses in other
>> DTS share opps. How about changing the binding so multiple clocks could
>> be specified at once ("bus0", "bus1")? I think there is no need for a
>> bus device for each clock.
> 
> The your commented method is possible.
> 
> But, I focus on implementing the generic bus frequency driver.
> 
> If specific bus device-tree node includes the one more clocks,
> when adding the new Exynos SoC, the exynos-bus.c should be added
> for new Exynos SoC. Because, each Exynos SoC has the different
> set of bus device.
> 
> If we use my approach, we don't need to modify the exynos-bus.c
> driver to support for the bus frequency of new Exynos SoC.

This won't change. The driver will just support from 1 to N clocks for
given bus device and set the same OPP to all of them. This will only
limit the number of duplicated entries. This won't affect the generic
approach of driver itself.

Best regards,
Krzysztof

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