Re: [PATCH] i2c: davinci: Fix null dereference bug in i2c_davinci_calc_clk_dividers

[Ben Dooks <ben-i2c-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org>]

On Sat, Apr 23, 2011 at 01:31:35PM -0400, Michael Williamson wrote:
> The davinci-i2c bus driver currently supports being probed with a NULL
> platform_data structure by using a default configuration when none is
> provided.  However, the i2c_davinci_calc_clk_dividers does not
> check the provided platform_data for NULL prior to using it, so
> the support is incomplete.
> 
> Rather than have each runtime call check for NULL and avoid future
> problems, copy a pointer to the default data to the device structure
> during the probe.  This should be OK, as the information in this
> structure is not modified by the driver.
> 
> Tested on a MityDSP-L138 module (OMAP-L138 based SOM).
> 
> Signed-off-by: Micahel Williamson <michael.williamson-wZX4cNJlHJ2sVWG7oymsAA@public.gmane.org>
> ---
>  drivers/i2c/busses/i2c-davinci.c |   12 +++++-------
>  1 files changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
> index 5795c83..1db8fc9 100644
> --- a/drivers/i2c/busses/i2c-davinci.c
> +++ b/drivers/i2c/busses/i2c-davinci.c
> @@ -163,8 +163,7 @@ static void i2c_recover_bus(struct davinci_i2c_dev *dev)
>  	flag |=  DAVINCI_I2C_MDR_NACK;
>  	/* write the data into mode register */
>  	davinci_i2c_write_reg(dev, DAVINCI_I2C_MDR_REG, flag);
> -	if (pdata)
> -		generic_i2c_clock_pulse(pdata->scl_pin);
> +	generic_i2c_clock_pulse(pdata->scl_pin);

This looks like a change in the behaviour of the code, since if there was
no pdata supplied we now can try generic_i2c_clock_pulse() with what is
probably gpio pin 0.

>  	/* Send STOP */
>  	flag = davinci_i2c_read_reg(dev, DAVINCI_I2C_MDR_REG);
>  	flag |= DAVINCI_I2C_MDR_STP;
> @@ -235,10 +234,11 @@ static void i2c_davinci_calc_clk_dividers(struct davinci_i2c_dev *dev)
>   */
>  static int i2c_davinci_init(struct davinci_i2c_dev *dev)
>  {
> -	struct davinci_i2c_platform_data *pdata = dev->dev->platform_data;
> +	struct davinci_i2c_platform_data *pdata;
>  
> -	if (!pdata)
> -		pdata = &davinci_i2c_platform_data_default;
> +	if (!dev->dev->platform_data)
> +		dev->dev->platform_data = &davinci_i2c_platform_data_default;
> +	pdata = dev->dev->platform_data;

Hmm, not going to work well if the driver is a module, as you'll unload
the module, leave the default pointer in and then re-load later at a
possibly different address with the old pointer in.
  
>  	/* put I2C into reset */
>  	davinci_i2c_reset_ctrl(dev, 0);
> @@ -313,8 +313,6 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg, int stop)
>  	u16 w;
>  	int r;
>  
> -	if (!pdata)
> -		pdata = &davinci_i2c_platform_data_default;
>  	/* Introduce a delay, required for some boards (e.g Davinci EVM) */
>  	if (pdata->bus_delay)
>  		udelay(pdata->bus_delay);
> -- 
> 1.7.0.4
> 
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-- 
Ben Dooks, ben-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org, http://www.fluff.org/ben/

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