cpts_calc_mult_shift() has a potential divide-by-zero in this line:

        do_div(maxsec, freq);

due to the fact that clk_get_rate() can return zero in certain error
conditions.
Add an explicit check to fix this.

Fixes: 88f0f0b0bebf ("net: ethernet: ti: cpts: calc mult and shift from refclk freq")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
---
This follows the same pattern as the fix in commit 7ca59947b5fc
("pwm: mediatek: Prevent divide-by-zero in pwm_mediatek_config()").
---
 drivers/net/ethernet/ti/cpts.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/ethernet/ti/cpts.c b/drivers/net/ethernet/ti/cpts.c
index 2ba4c8795d60..e4e3409e7648 100644
--- a/drivers/net/ethernet/ti/cpts.c
+++ b/drivers/net/ethernet/ti/cpts.c
@@ -607,6 +607,8 @@ static void cpts_calc_mult_shift(struct cpts *cpts)
 	u32 freq;
 
 	freq = clk_get_rate(cpts->refclk);
+	if (!freq)
+		return;
 
 	/* Calc the maximum number of seconds which we can run before
 	 * wrapping around.
-- 
2.39.5 (Apple Git-154)

On 28/08/2025 10:22, Miaoqian Lin wrote:
> cpts_calc_mult_shift() has a potential divide-by-zero in this line:
> 
>          do_div(maxsec, freq);
> 
> due to the fact that clk_get_rate() can return zero in certain error
> conditions.

Have you seen this happening in the real environment, or is it just
analysis of the code? I don't see a reason for these "certain error
conditions" to happen...

Hi, Vadim

Vadim Fedorenko <vadim.fedorenko@linux.dev> 于2025年8月28日周四 20:06写道：
>
> On 28/08/2025 10:22, Miaoqian Lin wrote:
> > cpts_calc_mult_shift() has a potential divide-by-zero in this line:
> >
> >          do_div(maxsec, freq);
> >
> > due to the fact that clk_get_rate() can return zero in certain error
> > conditions.
>
> Have you seen this happening in the real environment, or is it just
> analysis of the code? I don't see a reason for these "certain error
> conditions" to happen...

This is from code analysis, not from real environment.
The !CONFIG_HAVE_CLK version of clk_get_rate() returns zero.
With CONFIG_COMPILE_TEST && !CONFIG_HAVE_CLK could have the problem.
This may be theoretical.

On 28/08/2025 13:38, æå¦å© wrote:
> Hi, Vadim
> 
> Vadim Fedorenko <vadim.fedorenko@linux.dev> 于2025年8月28日周四 20:06写道：
>>
>> On 28/08/2025 10:22, Miaoqian Lin wrote:
>>> cpts_calc_mult_shift() has a potential divide-by-zero in this line:
>>>
>>>           do_div(maxsec, freq);
>>>
>>> due to the fact that clk_get_rate() can return zero in certain error
>>> conditions.
>>
>> Have you seen this happening in the real environment, or is it just
>> analysis of the code? I don't see a reason for these "certain error
>> conditions" to happen...
> 
> This is from code analysis, not from real environment.
> The !CONFIG_HAVE_CLK version of clk_get_rate() returns zero.
> With CONFIG_COMPILE_TEST && !CONFIG_HAVE_CLK could have the problem.
> This may be theoretical.

!CONFIG_HAVE_CLK will have cpts_create() doing nothing as defined in
cpts.h and it means the patch fixes impossible scenario.

NAck

On Thu, Aug 28, 2025 at 05:22:23PM +0800, Miaoqian Lin wrote:
> cpts_calc_mult_shift() has a potential divide-by-zero in this line:
> 
>         do_div(maxsec, freq);
> 
> due to the fact that clk_get_rate() can return zero in certain error
> conditions.
> Add an explicit check to fix this.
> 
> Fixes: 88f0f0b0bebf ("net: ethernet: ti: cpts: calc mult and shift from refclk freq")
> Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
> ---
> This follows the same pattern as the fix in commit 7ca59947b5fc
> ("pwm: mediatek: Prevent divide-by-zero in pwm_mediatek_config()").
> ---
>  drivers/net/ethernet/ti/cpts.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/ethernet/ti/cpts.c b/drivers/net/ethernet/ti/cpts.c
> index 2ba4c8795d60..e4e3409e7648 100644
> --- a/drivers/net/ethernet/ti/cpts.c
> +++ b/drivers/net/ethernet/ti/cpts.c
> @@ -607,6 +607,8 @@ static void cpts_calc_mult_shift(struct cpts *cpts)
>  	u32 freq;
>  
>  	freq = clk_get_rate(cpts->refclk);
> +	if (!freq)
> +		return;
>  
>  	/* Calc the maximum number of seconds which we can run before
>  	 * wrapping around.
> -- 
> 2.39.5 (Apple Git-154)
> 


Hi,

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