RE: [PATCH v2] i2c: tegra: Add delay before reset the controller
From: Alok Chauhan <hidden>
Date: 2012-02-14 05:49:58
Also in:
linux-i2c, lkml
Hi Shubhrajyot, On Mon, Dec 26, 2011 at 4:44 PM, Alok Chauhan [off-list ref] wrote:
quoted hunk ↗ jump to hunk
From: Alok Chauhan <redacted> 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 <redacted> --- 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.cb/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(structtegra_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. + */
quoted
quoted
quoted
Why do you need to reset the controller in case of a NACK.
This is required because of hardware limitations. Without reset we can't flus the internal hardware registers.
+ 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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