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

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Date:	Thu, 8 Mar 2012 11:59:23 +0530
From:	Alok Chauhan <alokc@...dia.com>
To:	Alok Chauhan <alokc@...dia.com>,
	Shubhrajyoti Datta <omaplinuxkernel@...il.com>
CC:	"khali@...ux-fr.org" <khali@...ux-fr.org>,
	"ben-linux@...ff.org" <ben-linux@...ff.org>,
	Stephen Warren <swarren@...dia.com>,
	"olof@...om.net" <olof@...om.net>,
	"bones@...retlab.ca" <bones@...retlab.ca>,
	"paul.gortmaker@...driver.com" <paul.gortmaker@...driver.com>,
	"dgreid@...gle.com" <dgreid@...gle.com>,
	Laxman Dewangan <ldewangan@...dia.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] i2c: tegra: Add delay before reset the controller

Hi all,

If there are no more concern then can we merge this patch to i2c tegra driver? 

Thanks
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.
>>>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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