gpio: Remove VLA from gpiolib
The new challenge is to remove VLAs from the kernel
(see https://lkml.org/lkml/2018/3/7/621) to eventually
turn on -Wvla.
Using a kmalloc array is the easy way to fix this but kmalloc is still
more expensive than stack allocation. Introduce a fast path with a
fixed size stack array to cover most chip with gpios below some fixed
amount. The slow path dynamically allocates an array to cover those
chips with a large number of gpios.
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Phil Reid <preid@electromag.com.au>
Reviewed-and-tested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Laura Abbott <labbott@redhat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index b960f6f..71c0ab4 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -22,6 +22,18 @@
if GPIOLIB
+config GPIOLIB_FASTPATH_LIMIT
+ int "Maximum number of GPIOs for fast path"
+ range 32 512
+ default 512
+ help
+ This adjusts the point at which certain APIs will switch from
+ using a stack allocated buffer to a dynamically allocated buffer.
+
+ You shouldn't need to change this unless you really need to
+ optimize either stack space or performance. Change this carefully
+ since setting an incorrect value could cause stack corruption.
+
config OF_GPIO
def_bool y
depends on OF
