linux-kernel - Re: [PATCH 1/4] clk: meson: Support PLL with fixed fractional denominators

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Message-ID: <9ef42da8-ac90-43de-8630-04cc8dc50783@amlogic.com>
Date: Fri, 6 Sep 2024 16:24:27 +0800
From: Chuan Liu <chuan.liu@...ogic.com>
To: Jerome Brunet <jbrunet@...libre.com>,
 Chuan Liu via B4 Relay <devnull+chuan.liu.amlogic.com@...nel.org>
Cc: Neil Armstrong <neil.armstrong@...aro.org>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, Kevin Hilman <khilman@...libre.com>,
 Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
 linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] clk: meson: Support PLL with fixed fractional
 denominators


On 2024/9/6 14:51, Jerome Brunet wrote:
> [ EXTERNAL EMAIL ]
>
> On Fri 06 Sep 2024 at 13:52, Chuan Liu via B4 Relay <devnull+chuan.liu.amlogic.com@...nel.org> wrote:
>
>> From: Chuan Liu <chuan.liu@...ogic.com>
>>
>> Some PLLs with fractional multipliers have fractional denominators that
>> are fixed to "100000" instead of the previous "(1 << pll->frac.width)".
>>
>> Signed-off-by: Chuan Liu <chuan.liu@...ogic.com>
>> ---
>>   drivers/clk/meson/clk-pll.c | 22 +++++++++++++++++++---
>>   drivers/clk/meson/clk-pll.h |  1 +
>>   2 files changed, 20 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/clk/meson/clk-pll.c b/drivers/clk/meson/clk-pll.c
>> index bc570a2ff3a3..f0009c174564 100644
>> --- a/drivers/clk/meson/clk-pll.c
>> +++ b/drivers/clk/meson/clk-pll.c
>> @@ -36,6 +36,12 @@
>>   #include "clk-regmap.h"
>>   #include "clk-pll.h"
>>
>> +/*
>> + * Some PLLs with fractional multipliers have fractional denominators that
>> + * are fixed to "100000" instead of the previous "(1 << pll->frac.width)".
>> + */
>> +#define FIXED_FRAC_MAX                       100000
> When the next arbitrary limit comes around, this will get very ugly.
> Instead, please add frac_max to the pll parameter


I also had this consideration before, and after confirmation, the
hifi_pll of the subsequent chip design will continue to be this value,
and the hifi_pll of the chip in recent years is also this value. So
let's define it here.

In the next version I replaced it with a member inside the structure
member of meson_clk_pll_data.


>
>> +
>>   static inline struct meson_clk_pll_data *
>>   meson_clk_pll_data(struct clk_regmap *clk)
>>   {
>> @@ -57,12 +63,17 @@ static unsigned long __pll_params_to_rate(unsigned long parent_rate,
>>                                          struct meson_clk_pll_data *pll)
>>   {
>>        u64 rate = (u64)parent_rate * m;
>> +     unsigned int frac_max;
>>
>>        if (frac && MESON_PARM_APPLICABLE(&pll->frac)) {
>>                u64 frac_rate = (u64)parent_rate * frac;
>>
>> -             rate += DIV_ROUND_UP_ULL(frac_rate,
>> -                                      (1 << pll->frac.width));
>> +             if (pll->flags & CLK_MESON_PLL_FIXED_FRAC_MAX)
>> +                     frac_max = FIXED_FRAC_MAX;
>> +             else
>> +                     frac_max = (1 << pll->frac.width);
>> +
>> +             rate += DIV_ROUND_UP_ULL(frac_rate, frac_max);
>>        }
>>
>>        return DIV_ROUND_UP_ULL(rate, n);
>> @@ -100,13 +111,18 @@ static unsigned int __pll_params_with_frac(unsigned long rate,
>>                                           unsigned int n,
>>                                           struct meson_clk_pll_data *pll)
>>   {
>> -     unsigned int frac_max = (1 << pll->frac.width);
>> +     unsigned int frac_max;
>>        u64 val = (u64)rate * n;
>>
>>        /* Bail out if we are already over the requested rate */
>>        if (rate < parent_rate * m / n)
>>                return 0;
>>
>> +     if (pll->flags & CLK_MESON_PLL_FIXED_FRAC_MAX)
> Certainly don't need a flag for that. Use a parameter and default to (1
> << pll->frac.width) if unset.
Okay
>
>> +             frac_max = FIXED_FRAC_MAX;
>> +     else
>> +             frac_max = (1 << pll->frac.width);
>> +
>>        if (pll->flags & CLK_MESON_PLL_ROUND_CLOSEST)
>>                val = DIV_ROUND_CLOSEST_ULL(val * frac_max, parent_rate);
>>        else
>> diff --git a/drivers/clk/meson/clk-pll.h b/drivers/clk/meson/clk-pll.h
>> index 7b6b87274073..e996d3727eb1 100644
>> --- a/drivers/clk/meson/clk-pll.h
>> +++ b/drivers/clk/meson/clk-pll.h
>> @@ -29,6 +29,7 @@ struct pll_mult_range {
>>
>>   #define CLK_MESON_PLL_ROUND_CLOSEST  BIT(0)
>>   #define CLK_MESON_PLL_NOINIT_ENABLED BIT(1)
>> +#define CLK_MESON_PLL_FIXED_FRAC_MAX BIT(2)
> Remove this.
>
>>   struct meson_clk_pll_data {
>>        struct parm en;
> --
> Jerome