linux-kernel - Re: [PATCH v6 1/3] clk: meson: add emmc sub clock phase delay driver

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Date:   Sun, 4 Nov 2018 23:12:17 +0800
From:   Jianxin Pan <jianxin.pan@...ogic.com>
To:     Stephen Boyd <sboyd@...nel.org>,
        Jerome Brunet <jbrunet@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>
CC:     Yixun Lan <yixun.lan@...ogic.com>,
        Kevin Hilman <khilman@...libre.com>,
        Carlo Caione <carlo@...one.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh@...nel.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Liang Yang <liang.yang@...ogic.com>,
        Jian Hu <jian.hu@...ogic.com>,
        Qiufang Dai <qiufang.dai@...ogic.com>,
        Hanjie Lin <hanjie.lin@...ogic.com>,
        Victor Wan <victor.wan@...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 v6 1/3] clk: meson: add emmc sub clock phase delay driver

Hi Stephen,

Thanks for your review. 
Please see me comments below.

On 2018/11/4 11:02, Stephen Boyd wrote:
> Quoting Jianxin Pan (2018-11-01 09:30:53)
>> diff --git a/drivers/clk/meson/clk-phase-delay.c b/drivers/clk/meson/clk-phase-delay.c
>> new file mode 100644
>> index 0000000..83e74ed
>> --- /dev/null
>> +++ b/drivers/clk/meson/clk-phase-delay.c
>> @@ -0,0 +1,66 @@
>> +// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
>> +/*
>> + * Amlogic Meson MMC Sub Clock Controller Driver
>> + *
>> + * Copyright (c) 2017 Baylibre SAS.
>> + * Author: Jerome Brunet <jbrunet@...libre.com>
>> + *
>> + * Copyright (c) 2018 Amlogic, inc.
>> + * Author: Yixun Lan <yixun.lan@...ogic.com>
>> + * Author: Jianxin Pan <jianxin.pan@...ogic.com>
>> + */
>> +
>> +#include <linux/clk-provider.h>
>> +#include "clkc.h"
>> +
>> +static int meson_clk_phase_delay_get_phase(struct clk_hw *hw)
>> +{
>> +       struct clk_regmap *clk = to_clk_regmap(hw);
>> +       struct meson_clk_phase_delay_data *ph =
>> +               meson_clk_get_phase_delay_data(clk);
> 
> Nitpick: Do this after declaring variables because it splits a line.
OK. I will split the assignment into another line. Thank you.
> 
>> +       unsigned long period_ps, p, d;
>> +       int degrees;
>> +
>> +       p = meson_parm_read(clk->map, &ph->phase);
>> +       degrees = p * 360 / (1 << (ph->phase.width));
> 
> Nitpick: Remove useless parenthesis.
OK. I will remove them.
> 
>> +
>> +       period_ps = DIV_ROUND_UP((unsigned long)NSEC_PER_SEC * 1000,
> 
> Is the cast necessary?
Yes, the cast can be droped. NSEC_PER_SEC is already defined wit type long.
> 
>> +                                clk_hw_get_rate(hw));
>> +
>> +       d = meson_parm_read(clk->map, &ph->delay);
>> +       degrees += d * ph->delay_step_ps * 360 / period_ps;
>> +       degrees %= 360;
>> +
>> +       return degrees;
>> +}
>> +
>> +static int meson_clk_phase_delay_set_phase(struct clk_hw *hw, int degrees)
>> +{
>> +       struct clk_regmap *clk = to_clk_regmap(hw);
>> +       struct meson_clk_phase_delay_data *ph =
>> +               meson_clk_get_phase_delay_data(clk);
>> +       unsigned long period_ps, d = 0, r;
>> +       u64 p;
>> +
>> +       p = degrees % 360;
> 
> We don't allow phase to be larger than 360 so this isn't needed.
OK, Thank you.
> 
>> +       period_ps = DIV_ROUND_UP((unsigned long)NSEC_PER_SEC * 1000,
> 
> Drop the cast?
OK.
> 
>> +                                clk_hw_get_rate(hw));
>> +
>> +       /* First compute the phase index (p), the remainder (r) is the
> 
> Nitpick: Please leave /* on it's own line.
OK.
> 
>> +        * part we'll try to acheive using the delays (d).
>> +        */
>> +       r = do_div(p, 360 / (1 << (ph->phase.width)));
> 
> Drop useless parenthesis please.
OK, I will fix it. Thank you.
> 
>> +       d = DIV_ROUND_CLOSEST(r * period_ps,
>> +                             360 * ph->delay_step_ps);
>> +       d = min(d, PMASK(ph->delay.width));
>> +
>> +       meson_parm_write(clk->map, &ph->phase, p);
>> +       meson_parm_write(clk->map, &ph->delay, d);
>> +       return 0;
>> +}
> 
> .
>