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

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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