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From:   Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
To:     David Woodhouse <dwmw2@infradead.org>,
        Brian Norris <computersforpeace@gmail.com>,
        Boris Brezillon <boris.brezillon@bootlin.com>,
        Marek Vasut <marek.vasut@gmail.com>,
        Richard Weinberger <richard@nod.at>,
        Zhouyang Jia <jiazhouyang09@gmail.com>,
        linux-mtd@lists.infradead.org,
        linux-kernel@vger.kernel.org (open list)
Cc:     Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Subject: [PATCH v2 5/8] mtd: maps: gpio-addr-flash: Replace array with an integer
Date:   Wed,  5 Sep 2018 16:36:40 +0200
Message-Id: <20180905143643.9871-6-ricardo.ribalda@gmail.com>
In-Reply-To: <20180905143643.9871-1-ricardo.ribalda@gmail.com>
References: <20180905143643.9871-1-ricardo.ribalda@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@gmail.com>
---
 drivers/mtd/maps/gpio-addr-flash.c | 31 +++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/drivers/mtd/maps/gpio-addr-flash.c b/drivers/mtd/maps/gpio-addr-flash.c
index 22e100f07112..8f5e3dce9be3 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;
 }
 
 /**
@@ -215,7 +218,7 @@ static int gpio_flash_probe(struct platform_device *pdev)
 	if (!memory || !gpios || !gpios->end)
 		return -EINVAL;
 
-	arr_size = sizeof(int) * gpios->end;
+	arr_size = sizeof(state->gpio_addrs[0]) * gpios->end;
 	state = devm_kzalloc(&pdev->dev, sizeof(*state) + arr_size, GFP_KERNEL);
 	if (!state)
 		return -ENOMEM;
@@ -226,9 +229,7 @@ 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;
-- 
2.18.0