linux-kernel - [PATCH] pinctrl: vt8500: wmt: constify gpio

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Date:   Tue, 11 Jul 2017 13:28:42 -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: vt8500: wmt: constify gpio_chip structure

This structure is only used to copy into other 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
   7754    2328       0   10082    2762 drivers/pinctrl/vt8500/pinctrl-wmt.o

after:
   text    data     bss     dec     hex filename
   7472    2272       0    9744    2610 drivers/pinctrl/vt8500/pinctrl-wmt.o

Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
---
 drivers/pinctrl/vt8500/pinctrl-wmt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pinctrl/vt8500/pinctrl-wmt.c b/drivers/pinctrl/vt8500/pinctrl-wmt.c
index c207e60..974e646 100644
--- a/drivers/pinctrl/vt8500/pinctrl-wmt.c
+++ b/drivers/pinctrl/vt8500/pinctrl-wmt.c
@@ -546,7 +546,7 @@ static int wmt_gpio_direction_output(struct gpio_chip *chip, unsigned offset,
 	return pinctrl_gpio_direction_output(chip->base + offset);
 }
 
-static struct gpio_chip wmt_gpio_chip = {
+static const struct gpio_chip wmt_gpio_chip = {
 	.label = "gpio-wmt",
 	.owner = THIS_MODULE,
 	.request = gpiochip_generic_request,
-- 
2.5.0