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

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Message-ID: <CAM=Q2cs+myCvph7OXvCDTG7y48oNTfRtjsDzQaKiEXzjdu3pzA@mail.gmail.com>
Date:	Fri, 10 Feb 2012 15:05:07 +0530
From:	Shubhrajyoti Datta <omaplinuxkernel@...il.com>
To:	Alok Chauhan <alokc@...dia.com>
Cc:	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,
	linux-tegra@...r.kernel.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] i2c: tegra: Add delay before reset the controller

Hello Alok,

On Mon, Dec 26, 2011 at 4:44 PM, Alok Chauhan <alokc@...dia.com> wrote:
> 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.
> +        */

Why do you need to reset the controller in case of a NACK.
> +       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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