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

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Message-ID: <4F6CF555.4080109@codeaurora.org>
Date:	Fri, 23 Mar 2012 15:12:37 -0700
From:	Saravana Kannan <skannan@...eaurora.org>
To:	"Turquette, Mike" <mturquette@...com>
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 03/23/2012 02:39 PM, Turquette, Mike wrote:
> On Fri, Mar 23, 2012 at 2:33 PM, Saravana Kannan<skannan@...eaurora.org>  wrote:
>> On 03/20/2012 08:10 PM, Saravana Kannan wrote:
>>>
>>> On 03/20/2012 04:53 PM, Turquette, Mike wrote:
>>>>
>>>> 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.
>>>
>>>
>>> I need to think a bit more about this.
>>
>>
>> I was thinking about this. I think the common clock fwk should let the
>> set_parent ops "return" the rate of the clock in addition to passing the
>> rate of the parent in.
>>
>> Say this is a divider clock and some one changes the parent. The cached
>> "rate" of the clock in the clock fwk is no longer correct. So, the clock fwk
>> should also add a "*new_rate" param to set parent ops.
>
> __clk_recalc_rates is called by __clk_reparent which is called by
> clk_set_parent.  __clk_recalc_rates is also called by clk_set_rate.
>
> Does this not handle the old cached clk->rate for you?

For the set_parent case, ops->recalc_rate() is called twice. Once for 
PRE_CHANGE and once for POST_CHANGE. For this clock, I can only really 
recalc the rate during the POST_CHANGE call. So, how should I 
differentiate the two cases?

On a separate note:
Sorry if I missed any earlier discussion on this, but what's the reason 
for calling recalc_rate() pre-change and post-change but without giving 
it the ability to differentiate between the two?

I think it's quite useful for recalc_rate to be called pre/post change 
(some steps have to be done pre/post change depending on whether the 
parent rate is increasing or decreasing). But I don't see the "msg" 
being passed along.

Also, I noticed that clk_set_parent() is treating a NULL as an invalid 
clock. Should that be fixed? set_parent(NULL) could be treated as a 
grounding the clock. Should we let the ops->set_parent determine if NULL 
is valid option?

Thanks,
Saravana

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