On Wed, Dec 21, 2022 at 07:59:00PM +0000, Hanna Hawa wrote:
> From: Lareine Khawaly <lareine@xxxxxxxxxx>
>
> In functions i2c_dw_scl_lcnt() and i2c_dw_scl_hcnt() may have overflow
> by depending on the values of the given parameters including the ic_clk.
> For example in our use case where ic_clk is larger than one million,
> multiplication of ic_clk * 4700 will result in 32 bit overflow.
>
> Add cast of u64 to the calculation to avoid multiplication overflow, and
> use the corresponding define for divide.
Perfect, thank you!
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Fixes: 2373f6b9744d ("i2c-designware: split of i2c-designware.c into core and bus specific parts")
> Signed-off-by: Lareine Khawaly <lareine@xxxxxxxxxx>
> Signed-off-by: Hanna Hawa <hhhawa@xxxxxxxxxx>
> ---
> Change log v4->v5:
> - Fix indentation
>
> Change Log v3->v4:
> - update line length when possible
> - fix change log location in the patch
>
> Change Log v2->v3:
> - Avoid changing the ic_clk parameter to u64, and do casting in the
> calculation itself instead.
> - i2c_dw_clk_rate() returns unsigned long which is confusing because the
> function return the value of get_clk_rate_khz() which returns u32.
> This is not effect the overflow issue, pushed change in separated
> patch.
> - use DIV_ROUND_CLOSEST_ULL instead of DIV_ROUND_CLOSEST
>
> Change Log v1->v2:
> - Update commit message and add fix tag.
>
> drivers/i2c/busses/i2c-designware-common.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-designware-common.c b/drivers/i2c/busses/i2c-designware-common.c
> index e0a46dfd1c15..6fdb25a5f801 100644
> --- a/drivers/i2c/busses/i2c-designware-common.c
> +++ b/drivers/i2c/busses/i2c-designware-common.c
> @@ -351,7 +351,8 @@ u32 i2c_dw_scl_hcnt(u32 ic_clk, u32 tSYMBOL, u32 tf, int cond, int offset)
> *
> * If your hardware is free from tHD;STA issue, try this one.
> */
> - return DIV_ROUND_CLOSEST(ic_clk * tSYMBOL, MICRO) - 8 + offset;
> + return DIV_ROUND_CLOSEST_ULL((u64)ic_clk * tSYMBOL, MICRO) -
> + 8 + offset;
> else
> /*
> * Conditional expression:
> @@ -367,7 +368,8 @@ u32 i2c_dw_scl_hcnt(u32 ic_clk, u32 tSYMBOL, u32 tf, int cond, int offset)
> * The reason why we need to take into account "tf" here,
> * is the same as described in i2c_dw_scl_lcnt().
> */
> - return DIV_ROUND_CLOSEST(ic_clk * (tSYMBOL + tf), MICRO) - 3 + offset;
> + return DIV_ROUND_CLOSEST_ULL((u64)ic_clk * (tSYMBOL + tf), MICRO) -
> + 3 + offset;
> }
>
> u32 i2c_dw_scl_lcnt(u32 ic_clk, u32 tLOW, u32 tf, int offset)
> @@ -383,7 +385,8 @@ u32 i2c_dw_scl_lcnt(u32 ic_clk, u32 tLOW, u32 tf, int offset)
> * account the fall time of SCL signal (tf). Default tf value
> * should be 0.3 us, for safety.
> */
> - return DIV_ROUND_CLOSEST(ic_clk * (tLOW + tf), MICRO) - 1 + offset;
> + return DIV_ROUND_CLOSEST_ULL((u64)ic_clk * (tLOW + tf), MICRO) -
> + 1 + offset;
> }
>
> int i2c_dw_set_sda_hold(struct dw_i2c_dev *dev)
> --
> 2.38.1
>
--
With Best Regards,
Andy Shevchenko
