linux-kernel - Re: [PATCH v2] clk: fixed-factor: add optional dt-binding clock-flags

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Date:	Mon, 4 Jul 2016 10:48:06 +0900
From:	Jongsung Kim <neidhard.kim@....com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Michael Turquette <mturquette@...libre.com>,
	Rob Herring <robh@...nel.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, Chanho Min <chanho.min@....com>
Subject: Re: [PATCH v2] clk: fixed-factor: add optional dt-binding clock-flags

On 2016년 07월 02일 09:20, Stephen Boyd wrote:
> On 06/29, Jongsung Kim wrote:
>> On 2016년 06월 29일 06:18, Michael Turquette wrote:
>>> Quoting Rob Herring (2016-06-28 13:55:18)
>>>> On Fri, Jun 24, 2016 at 01:12:52PM +0900, Jongsung Kim wrote:
>>>>> There is no way to set additional flags for a DT-initialized fixed-
>>>>> factor-clock, and it can be problematic i.e., when the clock rate
>>>>> needs to be changed. [1][2]
>>>>>
>>>>> This patch introduces an optional dt-binding named "clock-flags" to
>>>>> be used for passing any needed flags from dts.
>>>> I don't think we want this in DT. If we did, the flags would need some 
>>>> documentation about what the flags mean.
>>> Flags are specific to Linux implementation, so I agree with Rob. Better
>>> to create a compatible string for your hardware that bakes in the flags.
>> Thank you for your comment, Mike. This conversation starts from lacking method to set CLK_SET_RATE_PARENT from DT. I understand compatible string can be a solution. But.. if someone starts talking about lacking method to set another flag, i.e., CLK_SET_PARENT_GATE, then we'll need another compatible string list.
>> How do you think about defining possible required subset of the flags and using some more neutral flag-names acceptable in DT?
> Do you actually have an IC on the board that is doing some fixed
> factor calculation? Or is this a clk driver design where we are
> listing out each piece of an SoC's clk controller in DT?
>
The SoC has several PLLs of identical design, and one of them is divided
to half and used for CPUs. The fixed-factor-clock represents the divider.