[PATCH 3/4] clk: hisi: add stub clk driver

[Russell King - ARM Linux]

On Thu, Mar 26, 2015 at 07:13:38PM +0800, Leo Yan wrote:
> +static unsigned long hisi_stub_clk_recalc_rate(struct clk_hw *hw,
> +		unsigned long parent_rate)
> +{
...
> +	BUG_ON(!stub_clk->lock);
...

> +static int hisi_stub_clk_set_rate(struct clk_hw *hw, unsigned long rate,
> +                    unsigned long parent_rate)
> +{
...
> +	BUG_ON(!stub_clk->lock);
...

> +static long hisi_stub_clk_round_rate(struct clk_hw *hw, unsigned long rate,
> +		unsigned long *parent_rate)
> +{
...
> +	BUG_ON(!stub_clk->lock);
...

> +static struct clk_ops hisi_stub_clk_ops = {
> +	.recalc_rate	= hisi_stub_clk_recalc_rate,
> +	.round_rate	= hisi_stub_clk_round_rate,
> +	.set_rate	= hisi_stub_clk_set_rate,
> +};
...
> +static struct clk *_register_stub_clk(struct device *dev, unsigned int id,
> +	const char *name, const char *parent_name, unsigned long flags,
> +	spinlock_t *lock)
> +{
> +	struct hisi_stub_clk *stub_clk;
> +	struct clk *clk;
> +	struct clk_init_data init;
> +
> +	stub_clk = kzalloc(sizeof(*stub_clk), GFP_KERNEL);
> +	if (!stub_clk) {
> +		pr_err("%s: fail to alloc stub clk!\n", __func__);
> +		return ERR_PTR(-ENOMEM);
> +	}
> +
> +	init.name = name;
> +	init.ops = &hisi_stub_clk_ops;
> +	init.parent_names = parent_name ? &parent_name : NULL;
> +	init.num_parents = parent_name ? 1 : 0;
> +	init.flags = flags;
> +
> +	stub_clk->hw.init = &init;
> +	stub_clk->id = id;
> +	stub_clk->lock = lock;

Under what scenario is it safe to call _register_stub_clk() with a NULL
lock argument?

If lock is NULL, then every function callable via the ops structure
will bug.

Rather than doing a test in each method function, do it in
_register_stub_clk() - this means we aren't waiting for a NULL pointer
deref when one of these method functions gets called.

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