linux-kernel - Re: [PATCH v4 3/5] clk: add support for clock reparent on set

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Message-ID: <519C9A3D.1010902@imgtec.com>
Date:	Wed, 22 May 2013 11:13:17 +0100
From:	James Hogan <james.hogan@...tec.com>
To:	Saravana Kannan <skannan@...eaurora.org>
CC:	Mike Turquette <mturquette@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/5] clk: add support for clock reparent on set_rate

On 21/05/13 06:10, Saravana Kannan wrote:
> On 05/20/2013 06:28 AM, James Hogan wrote:
>> diff --git a/include/linux/clk-private.h b/include/linux/clk-private.h
>> index dd7adff..8138c94 100644
>> --- a/include/linux/clk-private.h
>> +++ b/include/linux/clk-private.h
>> @@ -33,8 +33,11 @@ struct clk {
>>       const char        **parent_names;
>>       struct clk        **parents;
>>       u8            num_parents;
>> +    u8            new_parent_index;
> 
> Why do you need this? Given the new_parent, can't the specific clock
> implementation just look it up when set_rate() is called? Wouldn't that
> be the only time you would actually need the index?
>
> If it's just for optimization of some error cases, I think we should
> drop this to keep the code simpler. One less state to keep track of when
> reading, writing or reviewing the clock framework.

clk_change_rate cannot currently return an error condition so I had
assumed it was better to check that the requested parent clock has a
valid parent index prior to starting to change any clock rates or firing
off any notifications.

Cheers
James

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