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

On Fri, Feb 04, 2011 at 08:04:03PM +0900, Jassi Brar wrote:

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

quoted

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.

No, I mean what I said.

The only way to do what you're asking is to attach a list of identifiers
which have prepared a clock to the struct clk, where each identifier is
unique to each driver instance.

So what that becomes is:

struct prepared_instance {
	struct list_head node;
	void *driver_id;
};

int clk_prepare(struct clk *clk, void *driver_id)
{
	struct prepared_instance *inst;
	int ret = 0;

	if (clk) {
		inst = kmalloc(sizeof(*inst), GFP_KERNEL);
		if (!inst)
			return -ENOMEM;

		inst->driver_id = driver_id;

		mutex_lock(&clk->mutex);
		if (clk->prepare_count++ = 0)
			ret = clk->ops->prepare(clk);

		if (ret = 0) {
			spin_lock_irqsave(&clk->lock, flags);
			list_add(&inst->node, &clk->prepare_list);
			spin_unlock_irqrestore(&clk->lock, flags);
		} else
			clk->prepare_count--;
		mutex_unlock(&clk->mutex);
	}
	return ret;
}

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

	if (clk) {
		struct prepare_instance *inst;

		spin_lock_irqsave(&clk->lock, flags);
		list_for_each_entry(inst, &clk->prepare_list, node)
			if (inst = driver_id)
				ret = -EINVAL;

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

I think that's going completely over the top, and adds needless complexity
to drivers, which now have to pass an instance specific cookie into every
clk API call.