[PATCH] pinctrl: Cleanup string initializations (char[] instead of char *)

[PATCH] pinctrl: Cleanup string initializations (char[] instead of char *)

[Manuel Schölling]

Initializations like 'char *foo = "bar"' will create two variables: a static
string and a pointer (foo) to that static string. Instead 'char foo[] = "bar"'
will declare a single variable and will end up in shorter
assembly (according to Jeff Garzik on the KernelJanitor's TODO list).

Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>
---
 drivers/pinctrl/pinctrl-mxs.c    |    6 +++---
 drivers/pinctrl/pinctrl-single.c |    4 ++--
 drivers/pinctrl/pinctrl-tegra.c  |    2 +-
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/pinctrl/pinctrl-mxs.c b/drivers/pinctrl/pinctrl-mxs.c
index 40c76f2..cd4215e 100644
--- a/drivers/pinctrl/pinctrl-mxs.c
+++ b/drivers/pinctrl/pinctrl-mxs.c
@@ -351,7 +351,7 @@ static int mxs_pinctrl_parse_group(struct platform_device *pdev,
 	struct mxs_pinctrl_data *d = platform_get_drvdata(pdev);
 	struct mxs_group *g = &d->soc->groups[idx];
 	struct property *prop;
-	const char *propname = "fsl,pinmux-ids";
+	const char propname[] = "fsl,pinmux-ids";
 	char *group;
 	int length = strlen(np->name) + SUFFIX_LEN;
 	u32 val, i;
@@ -399,8 +399,8 @@ static int mxs_pinctrl_probe_dt(struct platform_device *pdev,
 	struct device_node *np = pdev->dev.of_node;
 	struct device_node *child;
 	struct mxs_function *f;
-	const char *gpio_compat = "fsl,mxs-gpio";
-	const char *fn, *fnull = "";
+	const char gpio_compat[] = "fsl,mxs-gpio";
+	const char *fn, fnull[] = "";
 	int i = 0, idxf = 0, idxg = 0;
 	int ret;
 	u32 val;
diff --git a/drivers/pinctrl/pinctrl-single.c b/drivers/pinctrl/pinctrl-single.c
index 2960557..a3ed99f 100644
--- a/drivers/pinctrl/pinctrl-single.c
+++ b/drivers/pinctrl/pinctrl-single.c
@@ -1561,8 +1561,8 @@ static struct of_device_id pcs_of_match[];
 
 static int pcs_add_gpio_func(struct device_node *node, struct pcs_device *pcs)
 {
-	const char *propname = "pinctrl-single,gpio-range";
-	const char *cellname = "#pinctrl-single,gpio-range-cells";
+	const char propname[] = "pinctrl-single,gpio-range";
+	const char cellname[] = "#pinctrl-single,gpio-range-cells";
 	struct of_phandle_args gpiospec;
 	struct pcs_gpiofunc_range *range;
 	int ret, i;
diff --git a/drivers/pinctrl/pinctrl-tegra.c b/drivers/pinctrl/pinctrl-tegra.c
index 6545809..43eeb1b 100644
--- a/drivers/pinctrl/pinctrl-tegra.c
+++ b/drivers/pinctrl/pinctrl-tegra.c
@@ -576,7 +576,7 @@ static void tegra_pinconf_config_dbg_show(struct pinctrl_dev *pctldev,
 {
 	enum tegra_pinconf_param param = TEGRA_PINCONF_UNPACK_PARAM(config);
 	u16 arg = TEGRA_PINCONF_UNPACK_ARG(config);
-	const char *pname = "unknown";
+	const char pname[] = "unknown";
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(cfg_params); i++) {
-- 
1.7.10.4

Re: [PATCH] pinctrl: Cleanup string initializations (char[] instead of char *)

[Thierry Reding]

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On Sat, May 17, 2014 at 04:37:25PM +0200, Manuel Schölling wrote:
[...]
> diff --git a/drivers/pinctrl/pinctrl-tegra.c b/drivers/pinctrl/pinctrl-tegra.c
> index 6545809..43eeb1b 100644
> --- a/drivers/pinctrl/pinctrl-tegra.c
> +++ b/drivers/pinctrl/pinctrl-tegra.c
> @@ -576,7 +576,7 @@ static void tegra_pinconf_config_dbg_show(struct pinctrl_dev *pctldev,
>  {
>  	enum tegra_pinconf_param param = TEGRA_PINCONF_UNPACK_PARAM(config);
>  	u16 arg = TEGRA_PINCONF_UNPACK_ARG(config);
> -	const char *pname = "unknown";
> +	const char pname[] = "unknown";
>  	int i;
>  
>  	for (i = 0; i < ARRAY_SIZE(cfg_params); i++) {

When this hunk is applied, the build fails as follows:

  CC      drivers/pinctrl/pinctrl-tegra.o
drivers/pinctrl/pinctrl-tegra.c: In function 'tegra_pinconf_config_dbg_show':
drivers/pinctrl/pinctrl-tegra.c:589:4: warning: assignment of read-only location 'pname' [enabled by default]
    pname = cfg_params[i].property;
    ^
drivers/pinctrl/pinctrl-tegra.c:589:10: error: incompatible types when assigning to type 'const char[8]' from type 'const char * const'
    pname = cfg_params[i].property;
          ^

As you can see, pname is used to store a property name and the default
value is set to the static string "unknown" for cases where no matching
parameter is found in cfg_params. However, if a match is found the
default value will be overwritten, so you can't use const char [].

Thierry

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Re: [PATCH] pinctrl: Cleanup string initializations (char[] instead of char *)

[Linus Walleij]

On Sat, May 17, 2014 at 4:37 PM, Manuel Schölling
<manuel.schoelling@gmx.de> wrote:

> Initializations like 'char *foo = "bar"' will create two variables: a static
> string and a pointer (foo) to that static string. Instead 'char foo[] = "bar"'
> will declare a single variable and will end up in shorter
> assembly (according to Jeff Garzik on the KernelJanitor's TODO list).
>
> Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>

At this point of the release cycle I do not dare to apply this.

Please work in Thierry's errors and resend after the merge window.

Yours,
Linus Walleij