diff mbox series

clk: qcom: clk-rcg2: Fix wrong RCG clock rate for high parent frequencies

Message ID 20230720083304.28881-1-quic_devipriy@quicinc.com
State New
Headers
Series clk: qcom: clk-rcg2: Fix wrong RCG clock rate for high parent frequencies |

Commit Message

Devi Priya July 20, 2023, 8:33 a.m. UTC 
  If the parent clock rate is greater than unsigned long max/2 then
integer overflow happens when calculating the clock rate on 32-bit systems.
As RCG2 uses half integer dividers, the clock rate is first being
multiplied by 2 which will overflow the unsigned long max value. So, use
unsigned long long for rate computations to avoid overflow.

Signed-off-by: Devi Priya <quic_devipriy@quicinc.com>
---
 drivers/clk/qcom/clk-rcg2.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Comments

Konrad Dybcio July 20, 2023, 4:08 p.m. UTC | #1 
On 20.07.2023 10:33, Devi Priya wrote:
> If the parent clock rate is greater than unsigned long max/2 then
> integer overflow happens when calculating the clock rate on 32-bit systems.
> As RCG2 uses half integer dividers, the clock rate is first being
> multiplied by 2 which will overflow the unsigned long max value. So, use
> unsigned long long for rate computations to avoid overflow.
> 
> Signed-off-by: Devi Priya <quic_devipriy@quicinc.com>
> ---
>  drivers/clk/qcom/clk-rcg2.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
> index e22baf3a7112..42d00b134975 100644
> --- a/drivers/clk/qcom/clk-rcg2.c
> +++ b/drivers/clk/qcom/clk-rcg2.c
> @@ -156,18 +156,18 @@ static int clk_rcg2_set_parent(struct clk_hw *hw, u8 index)
>   *            hid_div       n
>   */
>  static unsigned long
> -calc_rate(unsigned long rate, u32 m, u32 n, u32 mode, u32 hid_div)
> +calc_rate(unsigned long parent_rate, u32 m, u32 n, u32 mode, u32 hid_div)
>  {
> +	u64 rate = parent_rate;
This should not be necessary.. You're being passed a copy of
the original value, which you can operate on.

Otherwise, LGTM

Konrad
Konrad Dybcio July 20, 2023, 4:08 p.m. UTC | #2 
On 20.07.2023 18:08, Konrad Dybcio wrote:
> On 20.07.2023 10:33, Devi Priya wrote:
>> If the parent clock rate is greater than unsigned long max/2 then
>> integer overflow happens when calculating the clock rate on 32-bit systems.
>> As RCG2 uses half integer dividers, the clock rate is first being
>> multiplied by 2 which will overflow the unsigned long max value. So, use
>> unsigned long long for rate computations to avoid overflow.
>>
>> Signed-off-by: Devi Priya <quic_devipriy@quicinc.com>
>> ---
>>  drivers/clk/qcom/clk-rcg2.c | 12 ++++++------
>>  1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
>> index e22baf3a7112..42d00b134975 100644
>> --- a/drivers/clk/qcom/clk-rcg2.c
>> +++ b/drivers/clk/qcom/clk-rcg2.c
>> @@ -156,18 +156,18 @@ static int clk_rcg2_set_parent(struct clk_hw *hw, u8 index)
>>   *            hid_div       n
>>   */
>>  static unsigned long
>> -calc_rate(unsigned long rate, u32 m, u32 n, u32 mode, u32 hid_div)
>> +calc_rate(unsigned long parent_rate, u32 m, u32 n, u32 mode, u32 hid_div)
>>  {
>> +	u64 rate = parent_rate;
> This should not be necessary.. You're being passed a copy of
> the original value, which you can operate on.
> 
> Otherwise, LGTM
Well obviously no, as I hit enter I realized this is of a different
type..

Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>

Konrad
Stephen Boyd July 20, 2023, 6:07 p.m. UTC | #3 
Quoting Devi Priya (2023-07-20 01:33:04)
> If the parent clock rate is greater than unsigned long max/2 then
> integer overflow happens when calculating the clock rate on 32-bit systems.
> As RCG2 uses half integer dividers, the clock rate is first being
> multiplied by 2 which will overflow the unsigned long max value. So, use
> unsigned long long for rate computations to avoid overflow.
> 
> Signed-off-by: Devi Priya <quic_devipriy@quicinc.com>
> ---

Any Fixes tag?
Marijn Suijten July 20, 2023, 7:07 p.m. UTC | #4 
Can you retitle this to state "overflow" rather than just "wrong"?
That's more descriptive.

E.g "Fix clockrate overflow for high parent frequencies"

On 2023-07-20 14:03:04, Devi Priya wrote:
> If the parent clock rate is greater than unsigned long max/2 then
> integer overflow happens when calculating the clock rate on 32-bit systems.
> As RCG2 uses half integer dividers, the clock rate is first being
> multiplied by 2 which will overflow the unsigned long max value. So, use
> unsigned long long for rate computations to avoid overflow.
> 
> Signed-off-by: Devi Priya <quic_devipriy@quicinc.com>
> ---
>  drivers/clk/qcom/clk-rcg2.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
> index e22baf3a7112..42d00b134975 100644
> --- a/drivers/clk/qcom/clk-rcg2.c
> +++ b/drivers/clk/qcom/clk-rcg2.c
> @@ -156,18 +156,18 @@ static int clk_rcg2_set_parent(struct clk_hw *hw, u8 index)
>   *            hid_div       n
>   */
>  static unsigned long
> -calc_rate(unsigned long rate, u32 m, u32 n, u32 mode, u32 hid_div)
> +calc_rate(unsigned long parent_rate, u32 m, u32 n, u32 mode, u32 hid_div)
>  {
> +	u64 rate = parent_rate;
> +
>  	if (hid_div) {
>  		rate *= 2;
> -		rate /= hid_div + 1;
> +		do_div(rate, hid_div + 1);

I'm pretty sure mult_frac() could have solved this as well, without
temporarily going to u64?

    mult_frac(rate, 2, hid_div + 1)

>  	}
>  
>  	if (mode) {
> -		u64 tmp = rate;
> -		tmp *= m;
> -		do_div(tmp, n);
> -		rate = tmp;
> +		rate *= m;
> +		do_div(rate, n);

    mult_frac(rate, m, n)

Or am I totally wrong?

- Marijn

>  	}
>  
>  	return rate;
> -- 
> 2.17.1
>
diff mbox series

Patch

diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
index e22baf3a7112..42d00b134975 100644
--- a/drivers/clk/qcom/clk-rcg2.c
+++ b/drivers/clk/qcom/clk-rcg2.c
@@ -156,18 +156,18 @@  static int clk_rcg2_set_parent(struct clk_hw *hw, u8 index)
  *            hid_div       n
  */
 static unsigned long
-calc_rate(unsigned long rate, u32 m, u32 n, u32 mode, u32 hid_div)
+calc_rate(unsigned long parent_rate, u32 m, u32 n, u32 mode, u32 hid_div)
 {
+	u64 rate = parent_rate;
+
 	if (hid_div) {
 		rate *= 2;
-		rate /= hid_div + 1;
+		do_div(rate, hid_div + 1);
 	}
 
 	if (mode) {
-		u64 tmp = rate;
-		tmp *= m;
-		do_div(tmp, n);
-		rate = tmp;
+		rate *= m;
+		do_div(rate, n);
 	}
 
 	return rate;