linux-kernel - [PATCH v5 5/8] mtd: maps: gpio-addr-flash: Replace array with an integer

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Date:   Wed,  3 Oct 2018 21:38:56 +0200
From:   Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
To:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Zhouyang Jia <jiazhouyang09@...il.com>,
        linux-mtd@...ts.infradead.org,
        open list <linux-kernel@...r.kernel.org>
Cc:     Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
Subject: [PATCH v5 5/8] mtd: maps: gpio-addr-flash: Replace array with an integer

By replacing the array with an integer we can avoid completely
the bit comparison loop if the value has not changed (by far
the most common case).

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
---
 drivers/mtd/maps/gpio-addr-flash.c | 34 +++++++++++++++---------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/drivers/mtd/maps/gpio-addr-flash.c b/drivers/mtd/maps/gpio-addr-flash.c
index 89cc8cce161b..47b12a6fead4 100644
--- a/drivers/mtd/maps/gpio-addr-flash.c
+++ b/drivers/mtd/maps/gpio-addr-flash.c
@@ -43,7 +43,7 @@ struct async_state {
 	struct map_info map;
 	size_t gpio_count;
 	unsigned *gpio_addrs;
-	int *gpio_values;
+	unsigned int gpio_values;
 	unsigned int win_order;
 };
 #define gf_map_info_to_state(mi) ((struct async_state *)(mi)->map_priv_1)
@@ -55,22 +55,25 @@ struct async_state {
  *
  * Rather than call the GPIO framework every time, cache the last-programmed
  * value.  This speeds up sequential accesses (which are by far the most common
- * type).  We rely on the GPIO framework to treat non-zero value as high so
- * that we don't have to normalize the bits.
+ * type).
  */
 static void gf_set_gpios(struct async_state *state, unsigned long ofs)
 {
-	size_t i = 0;
-	int value;
+	int i;
 
 	ofs >>= state->win_order;
-	do {
-		value = ofs & (1 << i);
-		if (state->gpio_values[i] != value) {
-			gpio_set_value(state->gpio_addrs[i], value);
-			state->gpio_values[i] = value;
-		}
-	} while (++i < state->gpio_count);
+
+	if (ofs == state->gpio_values)
+		return;
+
+	for (i = 0; i < state->gpio_count; i++) {
+		if ((ofs & BIT(i)) == (state->gpio_values & BIT(i)))
+			continue;
+
+		gpio_set_value(state->gpio_addrs[i], !!(ofs & BIT(i)));
+	}
+
+	state->gpio_values = ofs;
 }
 
 /**
@@ -202,7 +205,7 @@ static const char * const part_probe_types[] = {
  */
 static int gpio_flash_probe(struct platform_device *pdev)
 {
-	size_t i, arr_size;
+	size_t i;
 	struct physmap_flash_data *pdata;
 	struct resource *memory;
 	struct resource *gpios;
@@ -215,8 +218,7 @@ static int gpio_flash_probe(struct platform_device *pdev)
 	if (!memory || !gpios || !gpios->end)
 		return -EINVAL;
 
-	arr_size = sizeof(int) * gpios->end;
-	state = devm_kzalloc(&pdev->dev, sizeof(*state) + arr_size, GFP_KERNEL);
+	state = devm_kzalloc(&pdev->dev, sizeof(*state), GFP_KERNEL);
 	if (!state)
 		return -ENOMEM;
 
@@ -226,9 +228,7 @@ static int gpio_flash_probe(struct platform_device *pdev)
 	 */
 	state->gpio_count     = gpios->end;
 	state->gpio_addrs     = (void *)(unsigned long)gpios->start;
-	state->gpio_values    = (void *)(state + 1);
 	state->win_order      = get_bitmask_order(resource_size(memory)) - 1;
-	memset(state->gpio_values, 0xff, arr_size);
 
 	state->map.name       = DRIVER_NAME;
 	state->map.read       = gf_read;
-- 
2.19.0