Russell King - ARM Linux <li...@arm.linux.org.uk> writes:
> On Fri, Oct 16, 2009 at 12:09:17PM -0700, Kevin Hilman wrote:
>> From: Sekhar Nori <nsek...@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 <nsek...@ti.com>
>> Signed-off-by: Kevin Hilman <khil...@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.
On davinci, we only reparent during early init, so refusing to change
the parent of an enabled will suffice.
I've added a check (and warning) if the clock is already enabled as
well as a refusal to re-parent:
int clk_set_parent(struct clk *clk, struct clk *parent)
{
unsigned long flags;
if (clk == NULL || IS_ERR(clk))
return -EINVAL;
/* Cannot change parent on enabled clock */
if (WARN_ON(clk->usecount))
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);
spin_lock_irqsave(&clockfw_lock, flags);
if (clk->recalc)
clk->rate = clk->recalc(clk);
propagate_rate(clk);
spin_unlock_irqrestore(&clockfw_lock, flags);
return 0;
}
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