linux-kernel - [PATCH v2] i2c: tegra: Add delay before reset the controller

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Date:	Mon, 26 Dec 2011 16:44:41 +0530
From:	Alok Chauhan <alokc@...dia.com>
To:	khali@...ux-fr.org, ben-linux@...ff.org, swarren@...dia.com,
	olof@...om.net, bones@...retlab.ca, paul.gortmaker@...driver.com,
	dgreid@...gle.com, ldewangan@...dia.com
Cc:	linux-tegra@...r.kernel.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, Alok Chauhan <alokc@...dia.com>
Subject: [PATCH v2] i2c: tegra: Add delay before reset the controller

From: Alok Chauhan <alokc@...dia.com>

In NACK error condition, I2C controller violates
clock-to-data setup time before stop. In Software,
because of this reset of controller is happening
before I2C controller could complete STOP condition.

Added delay of 2 clock period before reset the
controller in case of NACK error.

Signed-off-by: Alok Chauhan <alokc@...dia.com>
---
Instead of setting constant value for delay as was in previous patch, now in
the current modification delay will be calculated based on clock frequency of the bus.
 drivers/i2c/busses/i2c-tegra.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
index 6381604..62e197c 100644
--- a/drivers/i2c/busses/i2c-tegra.c
+++ b/drivers/i2c/busses/i2c-tegra.c
@@ -517,6 +517,14 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
 	if (likely(i2c_dev->msg_err == I2C_ERR_NONE))
 		return 0;
 
+	/*
+	 * In NACK error condition resetting of I2C controller happens
+	 * before STOP condition is properly completed by I2C controller,
+	 * so wait for 2 clock cycle to complete STOP condition.
+	 */
+	if (i2c_dev->msg_err == I2C_ERR_NO_ACK)
+		udelay(DIV_ROUND_UP(2 * 1000000, i2c_dev->bus_clk_rate));
+
 	tegra_i2c_init(i2c_dev);
 	if (i2c_dev->msg_err == I2C_ERR_NO_ACK) {
 		if (msg->flags & I2C_M_IGNORE_NAK)
-- 
1.7.4.1

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