Re: [PATCH v9 5/6] clk: Add floor and ceiling constraints to clock rates
From: Tomeu Vizoso
Date: Thu Sep 04 2014 - 09:35:10 EST
On 09/04/2014 01:39 AM, Stephen Boyd wrote:
> On 09/03/14 08:33, Tomeu Vizoso wrote:
>> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
>> index 61a3492..3a961c6 100644
>> --- a/drivers/clk/clk.c
>> +++ b/drivers/clk/clk.c
>> @@ -560,6 +560,8 @@ struct clk *__clk_create_clk(struct clk_core *clk_core, const char *dev,
>> clk->dev_id = dev;
>> clk->con_id = con;
>> + hlist_add_head(&clk->child_node, &clk_core->per_user_clks);
> How is this safe with another thread that may be traversing the list? Or
> even two threads calling clk_get_parent() at the same time?
Good point, will take the prepare lock.
>> +int clk_set_floor_rate(struct clk *clk_user, unsigned long rate)
>> + struct clk_core *clk = clk_to_clk_core(clk_user);
>> + clk_user->floor_constraint = rate;
>> + return clk_provider_set_rate(clk, clk_provider_get_rate(clk));
> It would be nice if this was also locked around so that the
> floor_constraint or ceiling_constraint doesn't change while another
> thread is iterating the list. I guess we'll get by though because
> eventually things will settle and either this thread here will set the
> "final" rate, or the other thread in clk_provider_set_rate() will have
> already set the final rate. It just seems wrong to not hold the lock
> while updating what is supposed to be protected by the prepare lock.
Yeah, I also lean towards having an explicit lock, as having a more
deterministic behaviour can be quite helpful when debugging.
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