linux-kernel - [PATCH] i2c: designware: use {readl|writel}

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Date:	Thu, 11 Dec 2014 14:26:41 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	<wsa@...-dreams.de>, <linux-i2c@...r.kernel.org>
CC:	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	Jisheng Zhang <jszhang@...vell.com>
Subject: [PATCH] i2c: designware: use {readl|writel}_relaxed instead of readl/writel

readl/writel is too expensive especially on Cortex A9 w/ outer L2 cache.
This introduces i2c read/write errors on Marvell BG2/BG2Q SoCs when there
are heavy L2 cache maintenance operations at the same time.

The driver does not perform DMA, so it's safe to use the relaxed version.
>From another side, the relaxed io accessor macros are available on all
architectures now, so we can use the relaxed versions instead.

Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
---
 drivers/i2c/busses/i2c-designware-core.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
index 23628b7..e279948 100644
--- a/drivers/i2c/busses/i2c-designware-core.c
+++ b/drivers/i2c/busses/i2c-designware-core.c
@@ -170,10 +170,10 @@ u32 dw_readl(struct dw_i2c_dev *dev, int offset)
 	u32 value;
 
 	if (dev->accessor_flags & ACCESS_16BIT)
-		value = readw(dev->base + offset) |
-			(readw(dev->base + offset + 2) << 16);
+		value = readw_relaxed(dev->base + offset) |
+			(readw_relaxed(dev->base + offset + 2) << 16);
 	else
-		value = readl(dev->base + offset);
+		value = readl_relaxed(dev->base + offset);
 
 	if (dev->accessor_flags & ACCESS_SWAP)
 		return swab32(value);
@@ -187,10 +187,10 @@ void dw_writel(struct dw_i2c_dev *dev, u32 b, int offset)
 		b = swab32(b);
 
 	if (dev->accessor_flags & ACCESS_16BIT) {
-		writew((u16)b, dev->base + offset);
-		writew((u16)(b >> 16), dev->base + offset + 2);
+		writew_relaxed((u16)b, dev->base + offset);
+		writew_relaxed((u16)(b >> 16), dev->base + offset + 2);
 	} else {
-		writel(b, dev->base + offset);
+		writel_relaxed(b, dev->base + offset);
 	}
 }
 
-- 
2.1.3

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