Re: [PATCH] i2c: davinci: Fix null dereference bug in i2c_davinci_calc_clk_dividers
Hi Mr. Dooks,
On 5/2/2011 5:36 AM, Ben Dooks wrote:
> 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
>> ---
>> 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.
>
- There is a check in generic_i2c_clock_pulse() that does not allow for scl_pin
pin = 0. I didn't realize gpio pin 0 was a valid gpio when looking at it. Seems
like this is an issue as well?
- I think this code is always getting called. I don't think there are any
platforms that would work using a NULL pdata as i2c_davinci_calc_clk_dividers
would bomb. I don't see any platforms in mach-davinci that provide NULL
i2c platform_data. Perhaps I'm not looking hard enough.
>> /* 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.
>
I hadn't thought of (or tested) the load->unload->reload scenario.
Subtle (well, to me anyway). Thanks for pointing that out. Appreciate
your cycles on review.
>> /* 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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>
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[PATCH] i2c: davinci: Fix null dereference bug in i2c_davinci_calc_clk_dividers
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
---
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);
/* 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;
/* 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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Re: [PATCH] i2c-davinci: Fix use of default platform data if none supplied.
On 09/21/2010 08:24 PM, Ben Dooks wrote:
> On Sat, Sep 04, 2010 at 12:07:48PM -0400, Michael Williamson wrote:
>> There is a bug in the i2c-davinci device init routine that attempts
>> to use default platform data if none is supplied (e.g., is NULL).
>> This patch fixes the bug.
>>
>> Signed-off-by: Michael Williamson
>> ---
>> drivers/i2c/busses/i2c-davinci.c |8 +---
>> 1 files changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-davinci.c
>> b/drivers/i2c/busses/i2c-davinci.c
>> index c87..6d4eeeb 100644
>> --- a/drivers/i2c/busses/i2c-davinci.c
>> +++ b/drivers/i2c/busses/i2c-davinci.c
>> @@ -235,10 +235,12 @@ 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;
>
> At first glance this looks like a code shift, however is the platform
> data used later in the driver by referencing the device.platform_data
> field?
>
Yes. The problem call is i2c_davinci_calc_clk_dividers(), which is called
pretty early in the i2c_davinci_init() routine. There is a reference to
pdata->bus_freq without a check to see if pdata is valid. I think my proposed
fix is not the right approach as you have pointed out.
Perhaps a better patch would be (?):
---
diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
index c87..15d0cea 100644
--- a/drivers/i2c/busses/i2c-davinci.c
+++ b/drivers/i2c/busses/i2c-davinci.c
@@ -195,6 +195,9 @@ static void i2c_davinci_calc_clk_dividers(struct
davinci_i2c_dev *dev)
u32 clkl;
u32 input_clock = clk_get_rate(dev->clk);
+ if (!pdata)
+ pdata = &davinci_i2c_platform_data_default;
+
/* NOTE: I2C Clock divider programming info
* As per I2C specs the following formulas provide prescaler
* and low/high divider values
---
> Could you rewrite the header to show this, and if possible note any
> actual oops report that has been seen with this.
>
I found this because I was told (while proposing a new platform) to use NULL
as platform data as the parameters I was using matched the default data. I
didn't get an oops, it just hung (it's pretty early in the board init).
Our boot strapper/load resets the DDR where the kernel buffer is, so getting
any oops info is a bit time consuming. The above three lines (and the original
patch) resolved the problem.
I can update the header to indicate a default parameter set if you like. New
patch OK?
-Mike
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[PATCH] i2c-davinci: Fix use of default platform data if none supplied.
There is a bug in the i2c-davinci device init routine that attempts
to use default platform data if none is supplied (e.g., is NULL).
This patch fixes the bug.
Signed-off-by: Michael Williamson
---
drivers/i2c/busses/i2c-davinci.c |8 +---
1 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
index c87..6d4eeeb 100644
--- a/drivers/i2c/busses/i2c-davinci.c
+++ b/drivers/i2c/busses/i2c-davinci.c
@@ -235,10 +235,12 @@ 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;
/* put I2C into reset */
davinci_i2c_reset_ctrl(dev, 0);
--
1.7.0.4
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