linux-kernel - Re: [PATCH v7 2/3] clk: introduce the common clock framework

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Message-ID: <CAJOA=zNmgSQfYAUZ-vqqTk0w3s3eKz3tjVOpyDgO35Q_Ogkz0g@mail.gmail.com>
Date:	Tue, 20 Mar 2012 16:53:56 -0700
From:	"Turquette, Mike" <mturquette@...com>
To:	Saravana Kannan <skannan@...eaurora.org>
Cc:	Shawn Guo <shawn.guo@...aro.org>, Paul Walmsley <paul@...an.com>,
	Russell King <linux@....linux.org.uk>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	patches@...aro.org, Magnus Damm <magnus.damm@...il.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-kernel@...r.kernel.org, linaro-dev@...ts.linaro.org,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	linux-arm-kernel@...ts.infradead.org,
	Arnd Bergman <arnd.bergmann@...aro.org>
Subject: Re: [PATCH v7 2/3] clk: introduce the common clock framework

On Tue, Mar 20, 2012 at 10:46 AM, Saravana Kannan
<skannan@...eaurora.org> wrote:
> On Tue, March 20, 2012 7:02 am, Shawn Guo wrote:
>> On Thu, Mar 15, 2012 at 11:11:19PM -0700, Mike Turquette wrote:
>> ...
>>> +struct clk_ops {
>>> +    int             (*prepare)(struct clk_hw *hw);
>>> +    void            (*unprepare)(struct clk_hw *hw);
>>> +    int             (*enable)(struct clk_hw *hw);
>>> +    void            (*disable)(struct clk_hw *hw);
>>> +    int             (*is_enabled)(struct clk_hw *hw);
>>> +    unsigned long   (*recalc_rate)(struct clk_hw *hw,
>>> +                                    unsigned long parent_rate);
>>
>> I believe I have heard people love the interface with parent_rate
>> passed in.  I love that too.  But I would like to ask the same thing
>> on .round_rate and .set_rate as well for the same reason why we have
>> it for .recalc_rate.
>
> In my case, for most clocks, set rate involves reparenting. So, what does
> passing parent_rate for these even mean? Passing parent_rate seems more
> apt for recalc_rate since it's called when the parent rate changes -- so,
> the actual parent itself is not expected to change.

>From my conversations with folks across many platforms, I think that
the way your clock tree expects to change rates is the exception, not
the rule.  As such you should just ignore the parent_rate parameter as
it useless to you.

> I could ignore the parameter, but just wondering how many of the others
> see value in this. And if we do add this parameter, it shouldn't be made
> mandatory for the platform driver to use it (due to other assumptions the
> clock framework might make).

>From my rough census of folks that actually need .set_rate support, I
think that everyone except MSM could benefit from this.  Your concept
of clk_set_rate is everyone else's clk_set_parent.

Ignoring the new parameter should cause you no harm.  It does make me
wonder if it would be a good idea to pass in the parent rate for
.set_parent, which is analogous to .set_rate in many ways.

Regards,
Mike

> -Saravana
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