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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <7A0BFCFE3DA5CD47B0FB7984326F201A13689D386F@BGMAIL01.nvidia.com>
Date:	Tue, 14 Feb 2012 11:19:48 +0530
From:	Alok Chauhan <alokc@...dia.com>
To:	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 Shubhrajyot,

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
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-i2c" 
> in the body of a message to majordomo@...r.kernel.org More majordomo 
> info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/