| Message ID | 20230720083304.28881-1-quic_devipriy@quicinc.com |
|---|---|
| State | New |
| Headers | show |
| Series | clk: qcom: clk-rcg2: Fix wrong RCG clock rate for high parent frequencies | expand |
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
On 7/21/2023 12:37 AM, Marijn Suijten wrote: > Can you retitle this to state "overflow" rather than just "wrong"? > That's more descriptive. > > E.g "Fix clockrate overflow for high parent frequencies" Sure okay > > 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) Yes, sure will update > >> } >> >> if (mode) { >> - u64 tmp = rate; >> - tmp *= m; >> - do_div(tmp, n); >> - rate = tmp; >> + rate *= m; >> + do_div(rate, n); > > mult_frac(rate, m, n) Will update in V2 Thanks, Devi Priya > > Or am I totally wrong? > > - Marijn > >> } >> >> return rate; >> -- >> 2.17.1 >>
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;
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(-)