linux-kernel - [PATCH 1/4] i2c: tegra: make sure register writes completes

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Date:	Tue, 5 Jun 2012 18:39:57 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	<khali@...ux-fr.org>, <w.sang@...gutronix.de>,
	<ben-linux@...ff.org>, <swarren@...dotorg.org>, <olof@...om.net>
CC:	<linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-tegra@...r.kernel.org>,
	Laxman Dewangan <ldewangan@...dia.com>
Subject: [PATCH 1/4] i2c: tegra: make sure register writes completes

The Tegra PPSB (an peripheral bus) queues writes transactions.
In order to guarantee that writes have completed before a
certain time, a read transaction to a register on the same
bus must be executed.
This is necessary in situations such as when clearing an
interrupt status or enable, so that when returning from an
interrupt handler, the HW has already de-asserted its
interrupt status output, which will avoid spurious interrupts.

Signed-off-by: Laxman Dewangan <ldewangan@...dia.com>
---
 drivers/i2c/busses/i2c-tegra.c |   13 +++++++++++++
 1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
index 8b2e555..fa92396 100644
--- a/drivers/i2c/busses/i2c-tegra.c
+++ b/drivers/i2c/busses/i2c-tegra.c
@@ -430,6 +430,13 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
 	if (i2c_dev->is_dvc)
 		dvc_writel(i2c_dev, DVC_STATUS_I2C_DONE_INTR, DVC_STATUS);
 
+	/*
+	 * Register write get queued in the PPSB bus and write can
+	 * happen later. Read back register to make sure that register
+	 * write is completed.
+	 */
+	i2c_readl(i2c_dev, I2C_INT_STATUS);
+
 	if (status & I2C_INT_PACKET_XFER_COMPLETE) {
 		BUG_ON(i2c_dev->msg_buf_remaining);
 		complete(&i2c_dev->msg_complete);
@@ -444,6 +451,9 @@ err:
 	if (i2c_dev->is_dvc)
 		dvc_writel(i2c_dev, DVC_STATUS_I2C_DONE_INTR, DVC_STATUS);
 
+	/* Read back register to make sure that register writes completed */
+	i2c_readl(i2c_dev, I2C_INT_STATUS);
+
 	complete(&i2c_dev->msg_complete);
 	return IRQ_HANDLED;
 }
@@ -505,6 +515,9 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
 	ret = wait_for_completion_timeout(&i2c_dev->msg_complete, TEGRA_I2C_TIMEOUT);
 	tegra_i2c_mask_irq(i2c_dev, int_mask);
 
+	/* Read back register to make sure that register writes completed */
+	i2c_readl(i2c_dev, I2C_INT_MASK);
+
 	if (WARN_ON(ret == 0)) {
 		dev_err(i2c_dev->dev, "i2c transfer timed out\n");
 
-- 
1.7.1.1

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