[PATCH 5/5] gpiolib: avoid krealloc() in gpiod_get_array()

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

Instead of allocating descs before the loop and reallocating it via
krealloc() when candidate hardware array matching is detected on the
first iteration, defer allocation of descs until the first descriptor
is retrieved.

Factor descriptor allocation and fast-path validation into helper
functions gpio_descs_alloc() and gpio_descs_check_fastpath(). Inside
the loop, acquire the descriptor using __free(gpiod_put), allocate
descs once on the first iteration, check fast-path candidate
suitability, and transfer descriptor ownership using no_free_ptr().

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/gpio/gpiolib.c | 184 ++++++++++++++++++++++-------------------
 1 file changed, 99 insertions(+), 85 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 79f3be30ace1..177ca7748dae 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -5171,6 +5171,90 @@ static void gpiochip_free_hogs(struct gpio_chip *gc)
 		gpiochip_free_own_desc(desc);
 }
 
+static struct gpio_descs *gpio_descs_alloc(unsigned int count, struct gpio_desc *first_desc)
+{
+	struct gpio_device *gdev = gpiod_to_gpio_device(first_desc);
+	struct gpio_array *array_info;
+	struct gpio_descs *descs;
+	size_t descs_size, alloc_size;
+	unsigned int bitmap_size;
+
+	/*
+	 * If pin hardware number of array member 0 is also 0, select
+	 * its chip as a candidate for fast bitmap processing path.
+	 */
+	if (gpiod_hwgpio(first_desc) != 0)
+		return kzalloc_flex(*descs, desc, count);
+
+	descs_size = struct_size(descs, desc, count);
+	bitmap_size = BITS_TO_LONGS(max(gdev->ngpio, count));
+	alloc_size = descs_size + struct_size(array_info, invert_mask, 3 * bitmap_size);
+
+	descs = kzalloc(alloc_size, GFP_KERNEL);
+	if (!descs)
+		return NULL;
+
+	array_info = (void *)descs + descs_size;
+	array_info->get_mask = array_info->invert_mask + bitmap_size;
+	array_info->set_mask = array_info->get_mask + bitmap_size;
+
+	array_info->desc = descs->desc;
+	array_info->size = count;
+	array_info->gdev = gdev;
+	bitmap_set(array_info->get_mask, 0, count);
+	bitmap_set(array_info->set_mask, 0, count);
+	descs->info = array_info;
+
+	return descs;
+}
+
+static void gpio_descs_check_fastpath(struct gpio_descs *descs,
+				      struct gpio_desc *desc)
+{
+	struct gpio_array *array_info = descs->info;
+	unsigned int idx = descs->ndescs;
+	unsigned long dflags;
+
+	if (!array_info)
+		return;
+
+	/* Unmark array members which don't belong to the 'fast' chip */
+	if (array_info->gdev != gpiod_to_gpio_device(desc)) {
+		__clear_bit(idx, array_info->get_mask);
+		__clear_bit(idx, array_info->set_mask);
+		return;
+	}
+
+	/*
+	 * Detect array members which belong to the 'fast' chip
+	 * but their pins are not in hardware order.
+	 */
+	if (gpiod_hwgpio(desc) != idx) {
+		/*
+		 * Don't use fast path if all array members processed so
+		 * far belong to the same chip as this one but its pin
+		 * hardware number is different from its array index.
+		 */
+		if (bitmap_full(array_info->get_mask, idx)) {
+			descs->info = NULL;
+		} else {
+			__clear_bit(idx, array_info->get_mask);
+			__clear_bit(idx, array_info->set_mask);
+		}
+		return;
+	}
+
+	dflags = READ_ONCE(desc->flags);
+	/* Exclude open drain or open source from fast output */
+	if (test_bit(GPIOD_FLAG_OPEN_DRAIN, &dflags) ||
+	    test_bit(GPIOD_FLAG_OPEN_SOURCE, &dflags))
+		__clear_bit(idx, array_info->set_mask);
+
+	/* Identify 'fast' pins which require invertion */
+	if (gpiod_is_active_low(desc))
+		__set_bit(idx, array_info->invert_mask);
+}
+
 /**
  * gpiod_get_array - obtain multiple GPIOs from a multi-index GPIO function
  * @dev:	GPIO consumer, can be NULL for system-global GPIOs
@@ -5189,105 +5273,35 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
 						const char *con_id,
 						enum gpiod_flags flags)
 {
-	struct gpio_desc *desc;
-	struct gpio_device *gdev;
-	struct gpio_array *array_info = NULL;
-	int i, count, bitmap_size;
-	unsigned long dflags;
+	struct gpio_descs *descs __free(gpiod_put_array) = NULL;
+	int i, count;
 
 	count = gpiod_count(dev, con_id);
-	if (count < 0)
-		return ERR_PTR(count);
-
-	struct gpio_descs *descs __free(gpiod_put_array) =
-		kzalloc_flex(*descs, desc, count);
-	if (!descs)
-		return ERR_PTR(-ENOMEM);
+	if (count <= 0)
+		return ERR_PTR(count ?: -ENOENT);
 
 	for (i = 0; i < count; i++) {
-		desc = gpiod_get_index(dev, con_id, i, flags);
+		struct gpio_desc *desc __free(gpiod_put) =
+			gpiod_get_index(dev, con_id, i, flags);
 		if (IS_ERR(desc))
 			return ERR_CAST(desc);
 
-		descs->desc[descs->ndescs++] = desc;
-
-		gdev = gpiod_to_gpio_device(desc);
-		/*
-		 * If pin hardware number of array member 0 is also 0, select
-		 * its chip as a candidate for fast bitmap processing path.
-		 */
-		if (i == 0 && gpiod_hwgpio(desc) == 0) {
-			struct gpio_descs *array;
-			size_t descs_size = struct_size(descs, desc, count);
-
-			bitmap_size = BITS_TO_LONGS(gdev->ngpio > count ?
-						    gdev->ngpio : count);
-
-			array = krealloc(descs, descs_size +
-					 struct_size(array_info, invert_mask, 3 * bitmap_size),
-					 GFP_KERNEL | __GFP_ZERO);
-			if (!array)
+		if (i == 0) {
+			descs = gpio_descs_alloc(count, desc);
+			if (!descs)
 				return ERR_PTR(-ENOMEM);
-
-			descs = array;
-
-			array_info = (void *)descs + descs_size;
-			array_info->get_mask = array_info->invert_mask +
-						  bitmap_size;
-			array_info->set_mask = array_info->get_mask +
-						  bitmap_size;
-
-			array_info->desc = descs->desc;
-			array_info->size = count;
-			array_info->gdev = gdev;
-			bitmap_set(array_info->get_mask, 0, count);
-			bitmap_set(array_info->set_mask, 0, count);
-			descs->info = array_info;
 		}
 
-		/* If there is no cache for fast bitmap processing path, continue */
-		if (!array_info)
-			continue;
+		gpio_descs_check_fastpath(descs, desc);
 
-		/* Unmark array members which don't belong to the 'fast' chip */
-		if (array_info->gdev != gdev) {
-			__clear_bit(i, array_info->get_mask);
-			__clear_bit(i, array_info->set_mask);
-		}
-		/*
-		 * Detect array members which belong to the 'fast' chip
-		 * but their pins are not in hardware order.
-		 */
-		else if (gpiod_hwgpio(desc) != i) {
-			/*
-			 * Don't use fast path if all array members processed so
-			 * far belong to the same chip as this one but its pin
-			 * hardware number is different from its array index.
-			 */
-			if (bitmap_full(array_info->get_mask, i)) {
-				descs->info = NULL;
-				array_info = NULL;
-			} else {
-				__clear_bit(i, array_info->get_mask);
-				__clear_bit(i, array_info->set_mask);
-			}
-		} else {
-			dflags = READ_ONCE(desc->flags);
-			/* Exclude open drain or open source from fast output */
-			if (test_bit(GPIOD_FLAG_OPEN_DRAIN, &dflags) ||
-			    test_bit(GPIOD_FLAG_OPEN_SOURCE, &dflags))
-				__clear_bit(i, array_info->set_mask);
-			/* Identify 'fast' pins which require invertion */
-			if (gpiod_is_active_low(desc))
-				__set_bit(i, array_info->invert_mask);
-		}
+		descs->desc[descs->ndescs++] = no_free_ptr(desc);
 	}
-	if (array_info)
+	if (descs->info)
 		dev_dbg(dev,
 			"GPIO array info: chip=%s, size=%d, get_mask=%lx, set_mask=%lx, invert_mask=%lx\n",
-			array_info->gdev->label, array_info->size,
-			*array_info->get_mask, *array_info->set_mask,
-			*array_info->invert_mask);
+			descs->info->gdev->label, descs->info->size,
+			*descs->info->get_mask, *descs->info->set_mask,
+			*descs->info->invert_mask);
 	return_ptr(descs);
 }
 EXPORT_SYMBOL_GPL(gpiod_get_array);
-- 
2.56.0.307.g5fe7bd680c-goog