[PATCH v2 1/2] clk: Add of_clk_get_by_name_optional() function

From: geert@linux-m68k.org (Geert Uytterhoeven)
Date: 2018-07-30 08:56:09
Also in: linux-clk, lkml

Hi Phil,

On Mon, Jul 30, 2018 at 10:36 AM Phil Edworthy
[off-list ref] wrote:

Quite a few drivers get an optional clock, e.g. a clock required
to access peripheral's registers that is always enabled on some
devices.

This function behaves the same as of_clk_get_by_name() except that
it will return NULL instead of -ENOENT. This makes error checking
for users easier and allows clk_prepare_enable, etc to be called
on the returned reference without additional checks.

Signed-off-by: Phil Edworthy <redacted>

Thanks for your patch!

quoted hunk ↗ jump to hunk

--- a/drivers/clk/clkdev.c
+++ b/drivers/clk/clkdev.c

@@ -54,7 +54,8 @@ EXPORT_SYMBOL(of_clk_get);

 static struct clk *__of_clk_get_by_name(struct device_node *np,
                                        const char *dev_id,
-                                       const char *name)
+                                       const char *name,
+                                       bool optional)
 {
        struct clk *clk = ERR_PTR(-ENOENT);

@@ -73,6 +74,8 @@ static struct clk *__of_clk_get_by_name(struct device_node *np,
                if (!IS_ERR(clk)) {
                        break;
                } else if (name && index >= 0) {
+                       if (optional && PTR_ERR(clk) == -ENOENT)
+                               clk = NULL;

This only handles the "name && index >= 0" case.
If that condition is never true, the loop will end, eventually, and the last
value of clk will be returned. Hence there should be a similar check at the
end of the function.

                        if (PTR_ERR(clk) != -EPROBE_DEFER)
                                pr_err("ERROR: could not get clock %pOF:%s(%i)\n",
                                        np, name ? name : "", index);

Hence if not found, this will always print an error, even if the clock is
optional?

quoted hunk ↗ jump to hunk

@@ -106,15 +109,38 @@ struct clk *of_clk_get_by_name(struct device_node *np, const char *name)
        if (!np)
                return ERR_PTR(-ENOENT);

-       return __of_clk_get_by_name(np, np->full_name, name);
+       return __of_clk_get_by_name(np, np->full_name, name, false);
 }
 EXPORT_SYMBOL(of_clk_get_by_name);

+/**
+ * of_clk_get_by_name_optional() - Parse and lookup an optional clock referenced
+ * by a device node
+ * @np: pointer to clock consumer node
+ * @name: name of consumer's clock input, or NULL for the first clock reference
+ *
+ * This function parses the clocks and clock-names properties,
+ * and uses them to look up the struct clk from the registered list of clock
+ * providers.
+ * It behaves the same as of_clk_get_by_name(), except when no clock is found.
+ * In this case, instead of returning -ENOENT, it returns NULL.
+ */
+struct clk *of_clk_get_by_name_optional(struct device_node *np,
+                                       const char *name)
+{
+       if (!np)
+               return ERR_PTR(-ENOENT);

Shouldn't this return NULL?
Or let __of_clk_get_by_name() handle that (cfr. above)?

Hmm, of_clk_get_by_name() has a similar check, while the current
__of_clk_get_by_name() already handle np == NULL, too.

quoted hunk ↗ jump to hunk

+
+       return __of_clk_get_by_name(np, np->full_name, name, true);
+}
+EXPORT_SYMBOL(of_clk_get_by_name_optional);
+
 #else /* defined(CONFIG_OF) && defined(CONFIG_COMMON_CLK) */

 static struct clk *__of_clk_get_by_name(struct device_node *np,
                                        const char *dev_id,
-                                       const char *name)
+                                       const char *name,
+                                       bool optional)
 {
        return ERR_PTR(-ENOENT);
 }

@@ -197,7 +223,7 @@ struct clk *clk_get(struct device *dev, const char *con_id)
        struct clk *clk;

        if (dev && dev->of_node) {
-               clk = __of_clk_get_by_name(dev->of_node, dev_id, con_id);
+               clk = __of_clk_get_by_name(dev->of_node, dev_id, con_id, false);
                if (!IS_ERR(clk) || PTR_ERR(clk) == -EPROBE_DEFER)
                        return clk;
        }

diff --git a/include/linux/clk.h b/include/linux/clk.h
index 4f750c4..8cb5455 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h

@@ -777,6 +777,7 @@ static inline void clk_bulk_disable_unprepare(int num_clks,
 #if defined(CONFIG_OF) && defined(CONFIG_COMMON_CLK)
 struct clk *of_clk_get(struct device_node *np, int index);
 struct clk *of_clk_get_by_name(struct device_node *np, const char *name);
+struct clk *of_clk_get_by_name_optional(struct device_node *np, const char *name);
 struct clk *of_clk_get_from_provider(struct of_phandle_args *clkspec);
 #else
 static inline struct clk *of_clk_get(struct device_node *np, int index)

No dummy version of of_clk_get_by_name_optional() for the !CLK || !COMMON_CLK
case?

It seems of_clk_get_by_name() and of_clk_get_by_name_optional() can just
be simple wrappers around __of_clk_get_by_name(), differing only in the
value of the "optional" parameter. Hence I think it makes sense to move them
to the header file, and make them static inline.
Then only __of_clk_get_by_name() needs a (static inline) dummy for the !OF ||
!COMMON_CLK case.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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