| Message ID | 20240710074650.419902-2-thorsten.blum@toblux.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/i915: Explicitly cast divisor to fix Coccinelle warning | expand |
On Wed, Jul 10, 2024 at 09:46:51AM +0200, Thorsten Blum wrote: > As the comment explains, the if check ensures that the divisor oa_period > is a u32. Explicitly cast oa_period to u32 to remove the following > Coccinelle/coccicheck warning reported by do_div.cocci: > > WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead > > Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com> > --- > drivers/gpu/drm/i915/i915_perf.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c > index 0b1cd4c7a525..24722e758aaf 100644 > --- a/drivers/gpu/drm/i915/i915_perf.c > +++ b/drivers/gpu/drm/i915/i915_perf.c > @@ -4103,7 +4103,7 @@ static int read_properties_unlocked(struct i915_perf *perf, > */ > if (oa_period <= NSEC_PER_SEC) { > u64 tmp = NSEC_PER_SEC; > - do_div(tmp, oa_period); > + do_div(tmp, (u32)oa_period); Why is this code even using do_div() when it doesn't need the remainder? > oa_freq_hz = tmp; > } else > oa_freq_hz = 0; > -- > 2.45.2
On 10. Jul 2024, at 13:38, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote: > On Wed, Jul 10, 2024 at 09:46:51AM +0200, Thorsten Blum wrote: >> As the comment explains, the if check ensures that the divisor oa_period >> is a u32. Explicitly cast oa_period to u32 to remove the following >> Coccinelle/coccicheck warning reported by do_div.cocci: >> >> WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead >> >> Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com> >> --- >> drivers/gpu/drm/i915/i915_perf.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c >> index 0b1cd4c7a525..24722e758aaf 100644 >> --- a/drivers/gpu/drm/i915/i915_perf.c >> +++ b/drivers/gpu/drm/i915/i915_perf.c >> @@ -4103,7 +4103,7 @@ static int read_properties_unlocked(struct i915_perf *perf, >> */ >> if (oa_period <= NSEC_PER_SEC) { >> u64 tmp = NSEC_PER_SEC; >> - do_div(tmp, oa_period); >> + do_div(tmp, (u32)oa_period); > > Why is this code even using do_div() when it doesn't need the > remainder? do_div() is an optimized 64-by-32 division and the compiler should automatically remove the remainder if it's not used.
On Wed, Jul 10, 2024 at 01:55:32PM +0200, Thorsten Blum wrote: > On 10. Jul 2024, at 13:38, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote: > > On Wed, Jul 10, 2024 at 09:46:51AM +0200, Thorsten Blum wrote: > >> As the comment explains, the if check ensures that the divisor oa_period > >> is a u32. Explicitly cast oa_period to u32 to remove the following > >> Coccinelle/coccicheck warning reported by do_div.cocci: > >> > >> WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead > >> > >> Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com> > >> --- > >> drivers/gpu/drm/i915/i915_perf.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c > >> index 0b1cd4c7a525..24722e758aaf 100644 > >> --- a/drivers/gpu/drm/i915/i915_perf.c > >> +++ b/drivers/gpu/drm/i915/i915_perf.c > >> @@ -4103,7 +4103,7 @@ static int read_properties_unlocked(struct i915_perf *perf, > >> */ > >> if (oa_period <= NSEC_PER_SEC) { > >> u64 tmp = NSEC_PER_SEC; > >> - do_div(tmp, oa_period); > >> + do_div(tmp, (u32)oa_period); > > > > Why is this code even using do_div() when it doesn't need the > > remainder? > > do_div() is an optimized 64-by-32 division and the compiler should > automatically remove the remainder if it's not used. The point is that do_div() is a bad API because it magically changes the divided in place. There are more sensible 64bit division helpers in math64.h that can be used instead. oa_exponent_to_ns() also hand rolls a DIV_ROUND_UP_ULL() for some reason...
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c index 0b1cd4c7a525..24722e758aaf 100644 --- a/drivers/gpu/drm/i915/i915_perf.c +++ b/drivers/gpu/drm/i915/i915_perf.c @@ -4103,7 +4103,7 @@ static int read_properties_unlocked(struct i915_perf *perf, */ if (oa_period <= NSEC_PER_SEC) { u64 tmp = NSEC_PER_SEC; - do_div(tmp, oa_period); + do_div(tmp, (u32)oa_period); oa_freq_hz = tmp; } else oa_freq_hz = 0;
As the comment explains, the if check ensures that the divisor oa_period is a u32. Explicitly cast oa_period to u32 to remove the following Coccinelle/coccicheck warning reported by do_div.cocci: WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com> --- drivers/gpu/drm/i915/i915_perf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)