linux-kernel - Re: [PATCH v2] clk: Add fractional scale clock support

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Date:	Mon, 8 Aug 2016 16:40:41 -0700
From:	Hoan Tran <hotran@....com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Michael Turquette <mturquette@...libre.com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-clk <linux-clk@...r.kernel.org>, Duc Dang <dhdang@....com>,
	Loc Ho <lho@....com>
Subject: Re: [PATCH v2] clk: Add fractional scale clock support

On Wed, Jul 20, 2016 at 11:36 AM, Hoan Tran <hotran@....com> wrote:
> On Fri, Jul 1, 2016 at 5:09 PM, Hoan Tran <hotran@....com> wrote:
>>
>> Hi Stephen,
>>
>> On Fri, Jul 1, 2016 at 11:38 AM, Stephen Boyd <sboyd@...eaurora.org> wrote:
>> > Sorry I replied offlist before. Pressed the wrong key.
>> >
>> > On 06/30, Hoan Tran wrote:
>> >> On Thu, Jun 30, 2016 at 1:23 PM, Stephen Boyd <sboyd@...eaurora.org> wrote:
>> >> >
>> >> > How is this different from clk-fractional-divider.c?
>> >> >
>> >>
>> >> This is a driver which clock output is multiplied with a fixed fractional
>> >> scale (denominator).
>> >> A field inside a register is used to configure the multiplier.
>> >>
>> >> Example: With fractional scale is 1/8.
>> >> Freq_out = Freq_parent * multiplier * (1/8)
>> >>
>> >> For fractional-divider, there are 2 fields of a register are used which
>> >>  - A field for numerator
>> >>  - A field for denominator
>> >> Freq_out = Freq_parent * numerator / denominator
>> >>
>> >
>> > Ok so the difference is that the denominator is a fixed value?
>>
>> The major difference is a fixed denominator.
>> Another difference is:
>> In case CLK_FRACTIONAL_SCALE_INVERTED=1, the freq_out is calculated as below
>>
>> Freq_out = Freq_parent * (fixed_denominator - multiplier) / fixed_denominator.
>>
>> > Perhaps that can be modeled as a clk-multiplier that is used as
>> > the only parent of a fixed divider?
>>
>> Because of CLK_FRACTIONAL_SCALE_INVERTED flag, I don't know how to
>> model as a clk-multiplier. And how to pass the fixed denominator into
>> a clk-multiplier.
>>
>> > Or we can add a flag to the
>> > clk-fractional-divider code to handle this minor difference.
>>
>> This driver is used 2 register fields for numerator, denominator and
>> calculates both of them.
>> Do you think I can integrate this fractional scale into it ?
>>
>> Thanks
>> Hoan
>>
>
> Hi Stephen,
>
> Do you have any comments ?
>
> Thanks
> Hoan
>
>
>>
>> >
>> > --
>> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
>> > a Linux Foundation Collaborative Project

Hi Stephen,

Do you have any comments or suggestions on this patch ?

Thanks
Hoan