From: Wang Qing wangqing@vivo.com
do_div() does a 64-by-32 division. When the divisor is u64, do_div() truncates it to 32 bits, this means it can test non-zero and be truncated to zero for division.
fix do_div.cocci warning: do_div() does a 64-by-32 division, please consider using div64_u64 instead.
Signed-off-by: Wang Qing wangqing@vivo.com --- drivers/gpu/drm/msm/msm_gpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c index 2c1049c..aa4617b --- a/drivers/gpu/drm/msm/msm_gpu.c +++ b/drivers/gpu/drm/msm/msm_gpu.c @@ -648,7 +648,7 @@ static void retire_submit(struct msm_gpu *gpu, struct msm_ringbuffer *ring, /* Calculate the clock frequency from the number of CP cycles */ if (elapsed) { clock = (stats->cpcycles_end - stats->cpcycles_start) * 1000; - do_div(clock, elapsed); + div64_u64(clock, elapsed); }
trace_msm_gpu_submit_retired(submit, elapsed, clock,
On 09/02/2022 11:37, Qing Wang wrote:
From: Wang Qing wangqing@vivo.com
do_div() does a 64-by-32 division. When the divisor is u64, do_div() truncates it to 32 bits, this means it can test non-zero and be truncated to zero for division.
fix do_div.cocci warning: do_div() does a 64-by-32 division, please consider using div64_u64 instead.
Signed-off-by: Wang Qing wangqing@vivo.com
Reviewed-by: Dmitry Baryshkov dmitry.baryshkov@linaro.org
drivers/gpu/drm/msm/msm_gpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c index 2c1049c..aa4617b --- a/drivers/gpu/drm/msm/msm_gpu.c +++ b/drivers/gpu/drm/msm/msm_gpu.c @@ -648,7 +648,7 @@ static void retire_submit(struct msm_gpu *gpu, struct msm_ringbuffer *ring, /* Calculate the clock frequency from the number of CP cycles */ if (elapsed) { clock = (stats->cpcycles_end - stats->cpcycles_start) * 1000;
do_div(clock, elapsed);
div64_u64(clock, elapsed);}
trace_msm_gpu_submit_retired(submit, elapsed, clock,
On 10/02/2022 01:17, Dmitry Baryshkov wrote:
On 09/02/2022 11:37, Qing Wang wrote:
From: Wang Qing wangqing@vivo.com
do_div() does a 64-by-32 division. When the divisor is u64, do_div() truncates it to 32 bits, this means it can test non-zero and be truncated to zero for division.
fix do_div.cocci warning: do_div() does a 64-by-32 division, please consider using div64_u64 instead.
Signed-off-by: Wang Qing wangqing@vivo.com
Reviewed-by: Dmitry Baryshkov dmitry.baryshkov@linaro.org
After rechecking, I'd like to withdraw my R-B tag (Minecrell, thanks for pointing this out!)
The div64_u64 is not equivalent to do_div. It returns the quotient rather than modifying the first arg. Moreover it is unoptimal on 32-bit arches.
I'd suggest changing the math to remove multiplications by 1000 and 10000 before division. Or just ignoring this at all, judging from the fact that these values are used only for tracing rather than actual calculations.
drivers/gpu/drm/msm/msm_gpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c index 2c1049c..aa4617b --- a/drivers/gpu/drm/msm/msm_gpu.c +++ b/drivers/gpu/drm/msm/msm_gpu.c @@ -648,7 +648,7 @@ static void retire_submit(struct msm_gpu *gpu, struct msm_ringbuffer *ring, /* Calculate the clock frequency from the number of CP cycles */ if (elapsed) { clock = (stats->cpcycles_end - stats->cpcycles_start) * 1000; - do_div(clock, elapsed); + div64_u64(clock, elapsed); } trace_msm_gpu_submit_retired(submit, elapsed, clock,
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