linux-kernel - Re: [PATCH v3 2/2] clk: meson: add sub MMC clock controller driver

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Message-ID: <1e5f7ba3-59c1-27c8-89b7-cce87659462e@amlogic.com>
Date:   Thu, 9 Aug 2018 10:39:27 +0800
From:   Yixun Lan <yixun.lan@...ogic.com>
To:     Jerome Brunet <jbrunet@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Neil Armstrong <narmstrong@...libre.com>
CC:     <yixun.lan@...ogic.com>, Rob Herring <robh@...nel.org>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Kevin Hilman <khilman@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        <linux-kernel@...r.kernel.org>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Liang Yang <liang.yang@...ogic.com>,
        Qiufang Dai <qiufang.dai@...ogic.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Carlo Caione <carlo@...one.org>,
        <linux-amlogic@...ts.infradead.org>, <linux-clk@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Jian Hu <jian.hu@...ogic.com>
Subject: Re: [PATCH v3 2/2] clk: meson: add sub MMC clock controller driver

Hi Jerome

On 07/30/18 16:57, Jerome Brunet wrote:
> On Fri, 2018-07-27 at 09:45 -0700, Stephen Boyd wrote:
>> Quoting Stephen Boyd (2018-07-27 09:41:40)
>>> Quoting Yixun Lan (2018-07-27 07:52:23)
>>>> HI Stephen:
>>>>
>>>> On 07/26/2018 11:20 PM, Stephen Boyd wrote:
>>>>> Quoting Yixun Lan (2018-07-12 14:12:44)
>>>>>> diff --git a/drivers/clk/meson/mmc-clkc.c b/drivers/clk/meson/mmc-clkc.c
>>>>>> new file mode 100644
>>>>>> index 000000000000..36c4c7cd69a6
>>>>>> --- /dev/null
>>>>>> +++ b/drivers/clk/meson/mmc-clkc.c
>>>>>> @@ -0,0 +1,367 @@
>>>>>> +// 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>
>>>>>> + */
>>>>>> +
>>>>>> +#include <linux/clk.h>
>>>>>
>>>>> Is this include used?
>>>>>
>>>>
>>>> this is needed by clk_get_rate()
>>>> see drivers/clk/meson/mmc-clkc.c:204
>>>
>>> Hmm ok. That's unfortunate.
>>
>> You should be able to read the hardware to figure out the clk frequency?
>> This may be a sign that the phase clk_ops are bad and should be passing
>> in the frequency of the parent clk to the op so that phase can be
>> calculated. Jerome?
>>
> 
> It could be a away to do it but:
> a) if we modify the API, we would need to update every clock driver using it.
>    There is not that many users of the phase API but still, it is annoying
> b) This particular driver need the parent rate, other might need something else
> I guess. (parent phase ??, duty cycle ??) 
> 
> I think the real problem here it that you are using the consumer API. You should
> be using the provider API like clk_hw_get_rate. Look at the clk-divider.c which
> use clk_hw_round_rate() on the parent clock. 
I will replace it with clk_hw_get_rate()

> 
> Clock drivers should deal with 'struct clk_hw', not 'struct clk'. I think it was
> mentioned in the past that the 'clk' within 'struct clk_hw' might be removed
> someday.
> 
> Yixun, please don't put your clock driver within the controller driver. Please
> implement your 'phase-delay' clock in its own file and export the ops, like
> every other clock in the amlogic directory. Also, please review your list of
> '#define', some of them are unnecessary copy/paste from the MMC driver.
> 
will implement a clk-phase-delay.c

I can move the extra CC list

Yixun