linux-kernel - Re: [PATCH] i2c: tegra: Check for overflow errors with BUG

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Date:	Mon, 15 Aug 2011 22:17:46 +0300
From:	Felipe Balbi <balbi@...com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Ben Dooks <ben-linux@...ff.org>,
	Stephen Warren <swarren@...dia.com>,
	Vincent Palatin <vpalatin@...omium.org>,
	Rhyland Klein <rklein@...dia.com>,
	Jean Delvare <khali@...ux-fr.org>,
	Rakesh Iyer <riyer@...dia.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] i2c: tegra: Check for overflow errors with BUG_ON.

Hi,

On Mon, Aug 15, 2011 at 11:49:32AM -0700, Doug Anderson wrote:
> This change doesn't fix any known problems but turns
> on the overflow detection feature of the i2c controller
> in the hopes of flushing out any current (or future)
> bugs in the i2c driver.
> 
> Inspired by a change on nvidia's git server:
>   http://nv-tegra.nvidia.com/gitweb/?p=linux-2.6.git;a=commit;h=266d1b7397284505e55d06254b497cb32be07b69
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
>  drivers/i2c/busses/i2c-tegra.c |   11 ++++++++---
>  1 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index 2440b74..4dbba23 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -367,7 +367,8 @@ static int tegra_i2c_init(struct tegra_i2c_dev *i2c_dev)
>  static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
>  {
>  	u32 status;
> -	const u32 status_err = I2C_INT_NO_ACK | I2C_INT_ARBITRATION_LOST;
> +	const u32 status_err = I2C_INT_NO_ACK | I2C_INT_ARBITRATION_LOST |
> +		I2C_INT_TX_FIFO_OVERFLOW;
>  	struct tegra_i2c_dev *i2c_dev = dev_id;
>  
>  	status = i2c_readl(i2c_dev, I2C_INT_STATUS);
> @@ -389,6 +390,9 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
>  	}
>  
>  	if (unlikely(status & status_err)) {
> +		/* Don't pass this back--it can only happen due to a bug. */
> +		BUG_ON(status & I2C_INT_TX_FIFO_OVERFLOW);

so due to a FIFO overflow you lock up the whole system ? Can't you e.g.
reset the controller and reconfigure it rather than locking up the
system ?

-- 
balbi

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