clk: Allow parents to be specified via clkspec index

Some clk providers are simple DT nodes that only have a 'clocks'
property without having an associated 'clock-names' property. In these
cases, we want to let these clk providers point to their parent clks
without having to dereference the 'clocks' property at probe time to
figure out the parent's globally unique clk name. Let's add an 'index'
property to the parent_data structure so that clk providers can indicate
that their parent is a particular index in the 'clocks' DT property.

Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Jerome Brunet <jbrunet@baylibre.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Jeffrey Hugo <jhugo@codeaurora.org>
Cc: Chen-Yu Tsai <wens@csie.org>
Tested-by: Jeffrey Hugo <jhugo@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/clk.c

@@ -44,6 +44,7 @@ struct clk_parent_map {
 	struct clk_core		*core;
 	const char		*fw_name;
 	const char		*name;
+	int			index;
 };
 
 struct clk_core {
@@ -326,7 +327,8 @@ static struct clk_core *clk_core_lookup(const char *name)
 /**
  * clk_core_get - Find the clk_core parent of a clk
  * @core: clk to find parent of
- * @name: name to search for
+ * @name: name to search for (if string based)
+ * @index: index to use for search (if DT index based)
  *
  * This is the preferred method for clk providers to find the parent of a
  * clk when that parent is external to the clk controller. The parent_names
@@ -358,22 +360,23 @@ static struct clk_core *clk_core_lookup(const char *name)
  * provider knows about the clk but it isn't provided on this system.
  * A valid clk_core pointer when the clk can be found in the provider.
  */
-static struct clk_core *clk_core_get(struct clk_core *core, const char *name)
+static struct clk_core *clk_core_get(struct clk_core *core, const char *name,
+				     int index)
 {
 	struct clk_hw *hw = ERR_PTR(-ENOENT);
 	struct device *dev = core->dev;
 	const char *dev_id = dev ? dev_name(dev) : NULL;
 	struct device_node *np = core->of_node;
 
-	if (np)
-		hw = of_clk_get_hw(np, -1, name);
+	if (np && index >= 0)
+		hw = of_clk_get_hw(np, index, name);
 
 	/*
 	 * If the DT search above couldn't find the provider or the provider
 	 * didn't know about this clk, fallback to looking up via clkdev based
 	 * clk_lookups
 	 */
-	if (PTR_ERR(hw) == -ENOENT)
+	if (PTR_ERR(hw) == -ENOENT && name)
 		hw = clk_find_hw(dev_id, name);
 
 	if (IS_ERR(hw))
@@ -397,8 +400,7 @@ static void clk_core_fill_parent_index(struct clk_core *core, u8 index)
 		if (!parent)
 			parent = ERR_PTR(-EPROBE_DEFER);
 	} else {
-		if (entry->fw_name)
-			parent = clk_core_get(core, entry->fw_name);
+		parent = clk_core_get(core, entry->fw_name, entry->index);
 		if (IS_ERR(parent) && PTR_ERR(parent) == -ENOENT)
 			parent = clk_core_lookup(entry->name);
 	}
@@ -3443,6 +3445,7 @@ static int clk_core_populate_parent_map(struct clk_core *core)
 
 	/* Copy everything over because it might be __initdata */
 	for (i = 0, parent = parents; i < num_parents; i++, parent++) {
+		parent->index = -1;
 		if (parent_names) {
 			/* throw a WARN if any entries are NULL */
 			WARN(!parent_names[i],
@@ -3452,6 +3455,7 @@ static int clk_core_populate_parent_map(struct clk_core *core)
 					   true);
 		} else if (parent_data) {
 			parent->hw = parent_data[i].hw;
+			parent->index = parent_data[i].index;
 			ret = clk_cpy_name(&parent->fw_name,
 					   parent_data[i].fw_name, false);
 			if (!ret)

include/linux/clk-provider.h

@@ -255,11 +255,13 @@ struct clk_ops {
  * @hw: parent clk_hw pointer (used for clk providers with internal clks)
  * @fw_name: parent name local to provider registering clk
  * @name: globally unique parent name (used as a fallback)
+ * @index: parent index local to provider registering clk (if @fw_name absent)
  */
 struct clk_parent_data {
 	const struct clk_hw	*hw;
 	const char		*fw_name;
 	const char		*name;
+	int			index;
 };
 
 /**