Re: Locking in the clk API, part 2: clk_prepare/clk_unprepare

On Fri, Feb 4, 2011 at 7:48 PM, Russell King - ARM Linux
[off-list ref] wrote:

int clk_enable(struct clk *clk)
{
       unsigned long flags;
       int ret = 0;

       if (clk) {
               if (WARN_ON(!clk->prepare_count))
                       return -EINVAL;

               spin_lock_irqsave(&clk->lock, flags);
               if (clk->enable_count++ = 0)
                       ret = clk->ops->enable(clk);
               spin_unlock_irqrestore(&clk->lock, flags);
       }
       return ret;
}

is entirely sufficient to catch the case of a single-use clock not being
prepared before clk_enable() is called.

We're after detecting drivers missing calls to clk_prepare(), we're not
after detecting concurrent calls to clk_prepare()/clk_unprepare().

I hope you mean 'making sure the clock is prepared before it's enabled
' rather than
'catching a driver that doesn't do clk_prepare before clk_enable'.
Because, the above implementation still doesn't catch a driver that
doesn't call clk_prepare
but simply uses a clock that happens to have been already prepare'd by
some other
driver or the platform.