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

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Message-ID: <50950820.3050505@ti.com>
Date:	Sat, 3 Nov 2012 17:33:44 +0530
From:	Sekhar Nori <nsekhar@...com>
To:	Murali Karicheri <m-karicheri2@...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 11/2/2012 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.

> 
> +            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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