linux-kernel - Re: [PATCH v2 4/6] clk: hi6220: Clock driver support for Hisilicon hi6220 SoC

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Date:	Tue, 14 Apr 2015 16:53:45 +0800
From:	YiPing Xu <xuyiping@...ilicon.com>
To:	Arnd Bergmann <arnd@...db.de>,
	<linux-arm-kernel@...ts.infradead.org>
CC:	Bintian <bintian.wang@...wei.com>, <mark.rutland@....com>,
	<dan.zhao@...ilicon.com>, <btw@...l.itp.ac.cn>,
	<catalin.marinas@....com>, <wangbinghui@...ilicon.com>,
	<will.deacon@....com>, <huxinwei@...wei.com>,
	<haojian.zhuang@...aro.org>, <yanhaifeng@...il.com>,
	<rob.herring@...aro.org>, <mturquette@...aro.org>,
	<victor.lixin@...ilicon.com>, <xuwei5@...ilicon.com>,
	<jh80.chung@...sung.com>, <sledge.yanwei@...wei.com>,
	<kong.kongxinwei@...ilicon.com>, <heyunlei@...wei.com>,
	<puck.chen@...ilicon.com>, <zhangfei.gao@...aro.org>,
	<z.liuxinliang@...wei.com>, <devicetree@...r.kernel.org>,
	<khilman@...aro.org>, <pawel.moll@....com>,
	<ijc+devicetree@...lion.org.uk>, <tyler.baker@...aro.org>,
	<olof@...om.net>, <robh+dt@...nel.org>, <linux@....linux.org.uk>,
	<zhenwei.wang@...ilicon.com>, <w.f@...wei.com>,
	<guodong.xu@...aro.org>, <tomeu.vizoso@...labora.com>,
	<sboyd@...eaurora.org>, <linux-kernel@...r.kernel.org>,
	<galak@...eaurora.org>, <xuejiancheng@...wei.com>,
	<jorge.ramirez-ortiz@...aro.org>, <liguozhu@...ilicon.com>
Subject: Re: [PATCH v2 4/6] clk: hi6220: Clock driver support for Hisilicon
 hi6220 SoC

在 2015/4/13 23:34, Arnd Bergmann 写道:
> On Monday 13 April 2015 21:57:46 Bintian wrote:
>> Hello Arnd,
>>
>> Thanks for your code review.
>>
>> On 2015/4/13 21:30, Arnd Bergmann wrote:
>>> On Monday 13 April 2015 17:17:38 Bintian Wang wrote:
>>>> +#define HI6220_CFG_CSI2PHY     8
>>>> +#define HI6220_ISP_SCLK_GATE   9
>>>> +#define HI6220_ISP_SCLK_GATE1  10
>>>> +#define HI6220_ADE_CORE_GATE   11
>>>> +#define HI6220_CODEC_VPU_GATE  12
>>>> +#define HI6220_MED_SYSPLL      13
>>>> +
>>>> +/* mux clocks */
>>>> +#define HI6220_1440_1200       20
>>>> +#define HI6220_1000_1200       21
>>>> +#define HI6220_1000_1440       22
>>>> +
>>>> +/* divider clocks */
>>>> +#define HI6220_CODEC_JPEG      30
>>>> +#define HI6220_ISP_SCLK_SRC    31
>>>> +#define HI6220_ISP_SCLK1       32
>>>>
>>>
>>> The numbers seem rather arbitrary, and you have both holes as well as duplicate
>>> numbers here. I would suggest you do one of two things instead:
>
>> I just worry about some special clocks may be added later so keep some
>> holes for them;
>>
>> The duplicate numbers means clocks belong to different system control
>> domains.
>
> I don't understand. How would there be additional clocks added later?
> Wouldn't that be a new chip?

   There are some clocks not used in linux system. e.g, some clocks are 
used in base band processor. So, some numbers are not defined here.

> If you have separate system control domains, doesn't that mean that you
> also have separate DT bindings?
>
>>> a) have a separate header file per clock driver and make all the
>>>      numbers unique and consecutive within that header
>>>
>>> b) use the same numbers as the hardware registers so you can put the
>>>      numbers directly into the dts and don't need a header to create
>>>      an artificial ABI between the clock driver and the boot loader.
>> This header file will be used by device tree (I like using the clock
>> name instead "magic number" in dts :) )
>
> That's not how it works though: The dts file is the place to define
> the hardware numbers, we do that for all sorts of numbers: interrupts,
> gpios, register ranges etc are all defined in dts to avoid putting
> magic numbers in external header files.
>
> There are some cases where it gets too ugly for clock controllers
> that are highly irregular, but yours doesn't seem to be that kind.
>
> E.g. all the fixed rate clocks should just be separate device nodes,
> which lets you remove the binding for that node.
>
>> so how about keep them in one header file and let dts just include
>> one header file (not four files), but remove the holes?
>
> The header files constantly cause problems with merge dependencies,
> and we have some other companies that keep releasing new chips
> that each time require a new header file. If hisilicon plans to make
> more chips like this one, please consider coming up with more
> generic bindings to avoid this.
>
> 	Arnd
>
> .
>


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