[PATCH 13/46] davinci: support re-parenting a clock in the clock framework

[Kevin Hilman]

Russell King - ARM Linux <linux at arm.linux.org.uk> writes:

> On Fri, Oct 16, 2009 at 12:09:17PM -0700, Kevin Hilman wrote:
>> From: Sekhar Nori <nsekhar at ti.com>
>> 
>> The clk_set_parent() API is implemented to enable re-parenting
>> clocks in the clock tree.
>> 
>> This is useful in DVFS and helps by shifting clocks to an asynchronous
>> domain where supported by hardware
>> 
>> Signed-off-by: Sekhar Nori <nsekhar at ti.com>
>> Signed-off-by: Kevin Hilman <khilman at deeprootsystems.com>
>> ---
>>  arch/arm/mach-davinci/clock.c |   23 +++++++++++++++++++++++
>>  1 files changed, 23 insertions(+), 0 deletions(-)
>> 
>> diff --git a/arch/arm/mach-davinci/clock.c b/arch/arm/mach-davinci/clock.c
>> index 09e0e1c..12ceeea 100644
>> --- a/arch/arm/mach-davinci/clock.c
>> +++ b/arch/arm/mach-davinci/clock.c
>> @@ -141,6 +141,29 @@ int clk_set_rate(struct clk *clk, unsigned long rate)
>>  }
>>  EXPORT_SYMBOL(clk_set_rate);
>>  
>> +int clk_set_parent(struct clk *clk, struct clk *parent)
>> +{
>> +	unsigned long flags;
>> +
>> +	if (clk == NULL || IS_ERR(clk))
>> +		return -EINVAL;
>> +
>> +	mutex_lock(&clocks_mutex);
>> +	clk->parent = parent;
>> +	list_del_init(&clk->childnode);
>> +	list_add(&clk->childnode, &clk->parent->children);
>> +	mutex_unlock(&clocks_mutex);
>
> This is bad, and is suffering from precisely the same problem which
> OMAP suffered from:
>
> 1. it takes no notice of whether the clk is in use.
> 2. it takes no notice of whether the parent clocks are being used.
>
> The result is that using clk_set_parent() on a clk_enable()'d clock,
> you totally destroy the usecounting of the parent clocks, leading to
> the clock tree usecount becoming totally buggered up.
>
> Either refuse to change the parent of an already clk_enable()'d clock,
> or do proper usecount fixups when changing the parent.

Russell, thanks for the review.

Here's an updated version which refuses to reparent on an enabled
clock.  This updated one is now part of davinci-next.

Kevin