linux-kernel - Re: [PATCH v5 2/5] clk: meson: add support for A1 PLL clock ops

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Message-ID: <ee163cd0-a05e-5147-c307-e9870535b1dd@amlogic.com>
Date:   Thu, 9 Jan 2020 14:55:14 +0800
From:   Jian Hu <jian.hu@...ogic.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
CC:     Jerome Brunet <jbrunet@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Rob Herring <robh@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Qiufang Dai <qiufang.dai@...ogic.com>,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        Victor Wan <victor.wan@...ogic.com>,
        Chandle Zou <chandle.zou@...ogic.com>,
        <linux-clk@...r.kernel.org>, <linux-amlogic@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH v5 2/5] clk: meson: add support for A1 PLL clock ops

Hi Martin

Thanks for your review

On 2019/12/28 0:53, Martin Blumenstingl wrote:
> Hi Jian,
> 
> On Fri, Dec 27, 2019 at 10:46 AM Jian Hu <jian.hu@...ogic.com> wrote:
> [...]
>> @@ -294,9 +298,12 @@ static int meson_clk_pll_is_enabled(struct clk_hw *hw)
>>   {
>>          struct clk_regmap *clk = to_clk_regmap(hw);
>>          struct meson_clk_pll_data *pll = meson_clk_pll_data(clk);
>> +       int ret = 0;
>>
>> -       if (meson_parm_read(clk->map, &pll->rst) ||
>> -           !meson_parm_read(clk->map, &pll->en) ||
>> +       if (MESON_PARM_APPLICABLE(&pll->rst))
>> +               ret = meson_parm_read(clk->map, &pll->rst);
>> +
>> +       if (ret || !meson_parm_read(clk->map, &pll->en) ||
>>              !meson_parm_read(clk->map, &pll->l))
>>                  return 0;
> I had to read this part twice to understand what it's doing because I
> misunderstood what "ret" is used for (I thought that some "return ret"
> is missing)
> my proposal to make it easier to read:
> ...
> if (MESON_PARM_APPLICABLE(&pll->rst) &&
>      meson_parm_read(clk->map, &pll->rst))
>    return 0;
> 
> if (!meson_parm_read(clk->map, &pll->en) ||
>      !meson_parm_read(clk->map, &pll->l))
>                   return 0;
> ...
> 
> please let me know what you think about this
I was intended to use 'ret' to store the return value of pll->rst.

If pll->rst exists, it will get it. Otherwise, the ret will be zero.

Your proposal is a good way for it. I will use it.
> 
>> @@ -321,6 +328,23 @@ static int meson_clk_pll_enable(struct clk_hw *hw)
>>          /* do nothing if the PLL is already enabled */
>>          if (clk_hw_is_enabled(hw))
>>                  return 0;
>> +       /*
>> +        * Compared with the previous SoCs, self-adaption module current
>> +        * is newly added for A1, keep the new power-on sequence to enable the
>> +        * PLL.
>> +        */
>> +       if (MESON_PARM_APPLICABLE(&pll->current_en)) {
>> +               /* Enable the pll */
>> +               meson_parm_write(clk->map, &pll->en, 1);
>> +               udelay(10);
>> +               /* Enable the pll self-adaption module current */
>> +               meson_parm_write(clk->map, &pll->current_en, 1);
>> +               udelay(40);
>> +               /* Enable lock detect module */
>> +               meson_parm_write(clk->map, &pll->l_detect, 1);
>> +               meson_parm_write(clk->map, &pll->l_detect, 0);
>> +               goto out;
>> +       }
> in all other functions you are skipping the pll->rst register by
> checking for MESON_PARM_APPLICABLE(&pll->rst)
> I like that because it's a pattern which is easy to follow
> 
> do you think we can make this part consistent with that?
> I'm thinking of something like this (not compile-tested and I dropped
> all comments, just so you get the idea):
It is a good idea. I will test it.
> ...
> if (MESON_PARM_APPLICABLE(&pll->rst)
>    meson_parm_write(clk->map, &pll->rst, 1);
> 
> meson_parm_write(clk->map, &pll->en, 1);
> 
> if (MESON_PARM_APPLICABLE(&pll->rst))
>    meson_parm_write(clk->map, &pll->rst, 0);
> 
> if (MESON_PARM_APPLICABLE(&pll->current_en))
>    meson_parm_write(clk->map, &pll->current_en, 1);
> 
> if (MESON_PARM_APPLICABLE(&pll->l_detect)) {
>    meson_parm_write(clk->map, &pll->l_detect, 1);
>    meson_parm_write(clk->map, &pll->l_detect, 0);
> }
> 
> if (meson_clk_pll_wait_lock(hw))
> ...
> 
> I see two (and a half) benefits here:
> - if there's a PLL with neither the pll->current_en nor the pll->rst
> registers then you get support for this implementation for free
> - the if (MESON_PARM_APPLICABLE(...)) pattern is already used in the
> driver, but only for one register (in your example when
> MESON_PARM_APPLICABLE(&pll->current_en) exists you also modify the
> pll->l_detect register, which I did not expect)
> - only counts half: no use of "goto", which in my opinion makes it
> very easy to read (just read from top to bottom, checking each "if")
> 
I see, I will verify it.
> 
> Martin
> 
> .
>