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

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Message-ID: <20120106161803.GQ19115@trinity.fluff.org>
Date:	Fri, 6 Jan 2012 16:18:03 +0000
From:	Ben Dooks <ben-i2c@...ff.org>
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

On Mon, Dec 26, 2011 at 04:44:41PM +0530, Alok Chauhan 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.
> +	 */
> +	if (i2c_dev->msg_err == I2C_ERR_NO_ACK)
> +		udelay(DIV_ROUND_UP(2 * 1000000, i2c_dev->bus_clk_rate));
> +

Is a delay here good, would it be better to sleep so that some other
process can gain cpu time?

  	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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-- 
Ben Dooks, ben@...ff.org, http://www.fluff.org/ben/

Large Hadron Colada: A large Pina Colada that makes the universe disappear.

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