linux-kernel - [PATCH] pinctrl: coh901: constify gpio

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Date:   Tue, 11 Jul 2017 16:35:19 -0500
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Subject: [PATCH] pinctrl: coh901: constify gpio_chip structure

This structure is only used to copy into another structure, so declare
it as const.

This issue was detected using Coccinelle and the following semantic patch:

@r disable optional_qualifier@
identifier i;
position p;
@@
static struct gpio_chip i@p = { ... };

@ok@
identifier r.i;
expression e;
position p;
@@
e = i@p;

@bad@
position p != {r.p,ok.p};
identifier r.i;
struct gpio_chip e;
@@
e@i@p

@depends on !bad disable optional_qualifier@
identifier r.i;
@@
static
+const
 struct gpio_chip i = { ... };

In the following log you can see a significant difference in the code size
and data segment, hence in the dec segment. This log is the output
of the size command, before and after the code change:

before:
   text    data     bss     dec     hex filename
  12775    3696      64   16535    4097 drivers/pinctrl/pinctrl-coh901.o

after:
            bss     dec     hex filename
  12440    3640      64   16144    3f10 drivers/pinctrl/pinctrl-coh901.o

Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
---
 drivers/pinctrl/pinctrl-coh901.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pinctrl/pinctrl-coh901.c b/drivers/pinctrl/pinctrl-coh901.c
index 741b39e..ac155e7 100644
--- a/drivers/pinctrl/pinctrl-coh901.c
+++ b/drivers/pinctrl/pinctrl-coh901.c
@@ -387,7 +387,7 @@ int u300_gpio_config_set(struct gpio_chip *chip, unsigned offset,
 	return 0;
 }
 
-static struct gpio_chip u300_gpio_chip = {
+static const struct gpio_chip u300_gpio_chip = {
 	.label			= "u300-gpio-chip",
 	.owner			= THIS_MODULE,
 	.request		= gpiochip_generic_request,
-- 
2.5.0