linux-kernel - Re: [PATCH v1 1/2] clk: intel: Add CGU clock driver for a new SoC

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Message-ID: <CAHp75VdtsXjW5kaWVspi-5u6ya5512Yk7VN4HJ4Tn34PWci5Og@mail.gmail.com>
Date:   Sat, 7 Dec 2019 16:57:43 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     "Tanwar, Rahul" <rahul.tanwar@...ux.intel.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...el.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        robhkernel.org@...le.fi.intel.com,
        Mark Rutland <mark.rutland@....com>,
        linux-clk <linux-clk@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        qi-ming.wu@...el.com, yixin.zhu@...ux.intel.com,
        cheol.yong.kim@...el.com, rahul.tanwar@...el.com
Subject: Re: [PATCH v1 1/2] clk: intel: Add CGU clock driver for a new SoC

On Fri, Dec 6, 2019 at 7:06 AM Tanwar, Rahul
<rahul.tanwar@...ux.intel.com> wrote:
> On 2/9/2019 8:24 PM, Andy Shevchenko wrote:
> > On Mon, Sep 02, 2019 at 03:20:30PM +0300, Andy Shevchenko wrote:
> >> On Mon, Sep 02, 2019 at 03:43:13PM +0800, Tanwar, Rahul wrote:
> >>> On 28/8/2019 11:09 PM, Andy Shevchenko wrote:
> >>>> On Wed, Aug 28, 2019 at 03:00:17PM +0800, Rahul Tanwar wrote:

> >>>>> + { .val = 0, .div = 1 },
> >>>>> + { .val = 1, .div = 2 },
> >>>>> + { .val = 2, .div = 3 },
> >> 1
> >>
> >>>>> + { .val = 3, .div = 4 },
> >>>>> + { .val = 4, .div = 5 },
> >>>>> + { .val = 5, .div = 6 },
> >> 1
> >>
> >>>>> + { .val = 6, .div = 8 },
> >>>>> + { .val = 7, .div = 10 },
> >>>>> + { .val = 8, .div = 12 },
> >> 2
> >>
> >>>>> + { .val = 9, .div = 16 },
> >>>>> + { .val = 10, .div = 20 },
> >>>>> + { .val = 11, .div = 24 },
> >> 4
> >>
> >>>>> + { .val = 12, .div = 32 },
> >>>>> + { .val = 13, .div = 40 },
> >>>>> + { .val = 14, .div = 48 },
> >> 8
> >>
> >>>>> + { .val = 15, .div = 64 },
> >> 16
> >>
> >>
> >> So, now we see the pattern:
> >>
> >>      div = val < 3 ? (val + 1) : (1 << ((val - 3) / 3));
> > It's not complete, but I think you got the idea.
> >
> >> So, can we eliminate table?
>
> In the desperation to eliminate table, below is what i can come up with:
>
>         struct clk_div_table div_table[16];

But this is not an elimination, it's just a replacement from static to
dynamically calculated one.

>         int i, j;
>
>         for (i = 0; i < 16; i++)
>                 div_table[i].val = i;
>
>         for (i = 0, j=0; i < 16; i+=3, j++) {
>                 div_table[i].div = (i == 0) ? (1 << j) : (1 << (j + 1));
>                 if (i == 15)
>                         break;
>
>                 div_table[i + 1].div = (i == 0) ? ((1 << j) + 1) :
>                                         (1 << (j + 1)) + (1 << (j - 1));
>                 div_table[i + 2].div = (3 << j);
>         }
>
> To me, table still looks a better approach. Also, table is more extendable &
> consistent w.r.t. clk framework & other referenced clk drivers.
>
> Whats your opinion ?

Whatever CCF maintainers is fine with.

--
With Best Regards,
Andy Shevchenko