linux-kernel - Re: [PATCH v3 04/11] clk: davinci

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Message-ID: <5097D6DA.5050205@ti.com>
Date:	Mon, 5 Nov 2012 10:10:18 -0500
From:	Murali Karicheri <m-karicheri2@...com>
To:	Sekhar Nori <nsekhar@...com>
CC:	<mturquette@...aro.org>, <arnd@...db.de>,
	<akpm@...ux-foundation.org>, <shawn.guo@...aro.org>,
	<rob.herring@...xeda.com>, <linus.walleij@...aro.org>,
	<viresh.linux@...il.com>, <linux-kernel@...r.kernel.org>,
	<khilman@...com>, <linux@....linux.org.uk>, <sshtylyov@...sta.com>,
	<davinci-linux-open-source@...ux.davincidsp.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-keystone@...t.ti.com>
Subject: Re: [PATCH v3 04/11] clk: davinci - add pll divider clock driver

On 11/03/2012 08:03 AM, Sekhar Nori wrote:
> On 11/2/2012 7:23 PM, Murali Karicheri wrote:
>> On 11/02/2012 07:33 AM, Sekhar Nori wrote:
>>> On 10/25/2012 9:41 PM, Murali Karicheri wrote:
>>>
>>>> pll dividers are present in the pll controller of DaVinci and Other
>>>> SoCs that re-uses the same hardware IP. This has a enable bit for
>>>> bypass the divider or enable the driver. This is a sub class of the
>>>> clk-divider clock checks the enable bit to calculare the rate and
>>>> invoke the recalculate() function of the clk-divider if enabled.
>>>>
>>>> Signed-off-by: Murali Karicheri <m-karicheri2@...com>
>>>> ---
>>>> +/**
>>>> + * clk_register_davinci_plldiv - register function for DaVinci PLL
>>>> divider clk
>>>> + *
>>>> + * @dev: device ptr
>>>> + * @name: name of the clock
>>>> + * @parent_name: name of parent clock
>>>> + * @plldiv_data: ptr to pll divider data
>>>> + * @lock: ptr to spinlock passed to divider clock
>>>> + */
>>>> +struct clk *clk_register_davinci_plldiv(struct device *dev,
>>> Why do you need a dev pointer here and which device does it point to? In
>>> the only usage of this API in the series, you pass a NULL here. I should
>>> have probably asked this question on one of the earlier patches itself.
>>>
>> I did a grep in the drivers/clk directory. All of the platform drivers
>> are having the device ptr and all of them are called with NULL. I am not
>> sure what is the intent of this arg in the API.  As per documentation of
> I just took a look at the mxs example you referenced below and it does
> not take a dev pointer.
>
> struct clk *mxs_clk_div(const char *name, const char *parent_name,
>                          void __iomem *reg, u8 shift, u8 width, u8 busy)
> {
>
>> the clk_register() API, the device ptr points to the device that is
>> registering this clk. So if a specific device driver ever has to
>> register a PLL div clk, this will be non NULL. In  the normal use case,
>> clk is registered in a platform specific code and is always passed NULL.
>>
>> The platform/SoC specific clock initialization code will be using
>> davinci_plldiv_clk() that doesn't have a device ptr arg.
>> So this can be changed in future in sync with other drivers (assuming
>> this will get removed if unused), and changes
>> doesn't impact the platform code that initialize the clock. So IMO, we
>> should keep this arg so that it is in sync with other driver APIs.
> I think you should get rid of this unused arg and introduce it when you
> actually need it. That way we are clear about why we need it.
>
You are right. I will remove it and for other drivers.
>> +            const char *name, const char *parent_name,
>> +            struct clk_plldiv_data *plldiv_data,
>> +            spinlock_t *lock)
>> +{
>> +    struct clk_div *div;
>> +    struct clk *clk;
>> +    struct clk_init_data init;
>> +
>> +    div = kzalloc(sizeof(*div), GFP_KERNEL);
>> +    if (!div)
>> +        return ERR_PTR(-ENOMEM);
>> +
>> +    init.name = name;
>> +    init.ops = &clk_div_ops;
>> +    init.flags = plldiv_data->flags;
>> +    init.parent_names = (parent_name ? &parent_name : NULL);
>> +    init.num_parents = (parent_name ? 1 : 0);
>> +
>> +    div->reg = plldiv_data->reg;
>> +    div->en_id = plldiv_data->en_id;
>> +
>> +    div->divider.reg = plldiv_data->reg;
>> +    div->divider.shift = plldiv_data->shift;
>> +    div->divider.width = plldiv_data->width;
>> +    div->divider.flags = plldiv_data->divider_flags;
>> +    div->divider.lock = lock;
>> +    div->divider.hw.init = &init;
>> +    div->ops = &clk_divider_ops;
>> +
>> +    clk = clk_register(NULL, &div->divider.hw);
>>
>>> Shouldn't you be calling clk_register_divider() here which in turn will
>>> do clk_register()?
>> As stated in the top of the file, this is a subclass driver of clk-div
>> similar in line with mxs/clk-div.c. The
>> driver registers the clock instead of calling clk_register_divider() so
>> that it's ops function has a chance to do whatever it wants to do and
>> call the divider ops function after that.
> I see that now. I should have paid more attention.
>
> Regards,
> Sekhar
>

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