On 17/05/2018 08:00, Laura Abbott wrote:
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-and-tested-by: Lukas Wunner
Signed-off-by: Lukas Wunner
Signed-off-by: Laura Abbott
---
v6: Introduce a config option for setting the fast path GPIOs because
there are too many combinations to make the arch default workable. I
went with a default of 512 in the Kconfig.
Also to other points: I don't think the warning should be triggerable
from userspace, it should only happen on probe. I also think only
memsetting half the array is more likely to be error prone. We can
change it if there is significant overhead.
---
drivers/gpio/Kconfig | 10 +
drivers/gpio/gpiolib.c| 76 +++
drivers/gpio/gpiolib.h| 2 +-
include/linux/gpio/consumer.h | 10 +++--
4 files changed, 76 insertions(+), 22 deletions(-)
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 68d812b38be7..2855b5c5c8ca 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -22,6 +22,16 @@ menuconfig GPIOLIB
if GPIOLIB
+config GPIOLIB_FASTPATH_LIMIT
+ int "Maximum number of GPIOs for fast path"
+ default 512
+ help
+ This adjusts the point at which certain APIs will switch from
+ using a statically allocated fixed size buffer to a dynamically
+ allocated buffer. This is a trade-off in stackspace vs. speed.
+ You shouldn't need to change this unless you really need to
+ optimize one of those two.
+
config OF_GPIO
def_bool y
depends on OF
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index d66de67ef307..f7ce546796e0 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -61,6 +61,11 @@ static struct bus_type gpio_bus_type = {
.name = "gpio",
};
+/*
+ * Number of GPIOs to use for the fast path in set array
+ */
+#define FASTPATH_NGPIO CONFIG_GPIOLIB_FASTPATH_LIMIT
+
/* gpio_lock prevents conflicts during gpio_desc[] table updates.
* While any GPIO is requested, its gpio_chip is not removable;
* each GPIO's "requested" flag serves as a lock and refcount.
@@ -399,12 +404,11 @@ static long linehandle_ioctl(struct file *filep, unsigned
int cmd,
vals[i] = !!ghd.values[i];
/* Reuse the array setting function */
- gpiod_set_array_value_complex(false,
+ return gpiod_set_array_value_complex(false,
true,
lh->numdescs,
lh->descs,
vals);
- return 0;
}
return -EINVAL;
}
@@ -1192,6 +1196,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip,
void *data,
goto err_free_descs;
}
+ if (chip->ngpio > FASTPATH_NGPIO)
+ chip_warn(chip, "line cnt %d is greater than fast path cnt
%d\n",
+ chip->ngpio, FASTPATH_NGPIO);
+
gdev->label = kstrdup_const(chip->label ?: "unknown", GFP_KERNEL);
if (!gdev->label) {
status = -ENOMEM;
@@ -2662,16 +2670,28 @@ int gpiod_get_array_value_complex(bool raw, bool
can_sleep,
while (i < array_size) {
struct gpio_chip *chip = desc_array[i]->gdev->chip;
- unsigned long mask[BITS_TO_LONGS(chip->ngpio)];
- unsigned long bits[BITS_TO_LONGS(chip->ngpio)];
+ unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)];
+ unsigned long *mask, *bits;
int first, j, ret;
+ if (likely(chip->ngpio <= FASTPATH_NGPIO)) {
+ memset(fastpath, 0, sizeof(fastpath));
+ mask = fastpath;
+ bits = fastpath + BITS_TO_LONGS(FASTPATH_NGPIO);
+ } else {
+ mask = kcalloc(2 * BITS_TO_LONGS(chip->ngpio),
+ sizeof(*mask),
+ can_sleep ? GFP_KERNEL : GFP_ATOMIC);
+ if (!mask)
+ return -ENOMEM;
+ bits = mask + BITS_TO_LONGS(chip->ngpio);
+ }
+
if (!can_sleep)
WARN_ON(chip->can_sleep);
/* collect all inputs belonging to the same chip */
first = i;
- memset(mask, 0, sizeof(mask));
do {
const struct gpio_desc *desc = desc_array[i];