| Message ID | 20240802160323.46518-2-thorsten.blum@toblux.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] drm/i915: Explicitly cast divisor and use div_u64() | expand |
-----Original Message----- From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of Thorsten Blum Sent: Friday, August 2, 2024 9:03 AM To: jani.nikula@linux.intel.com; joonas.lahtinen@linux.intel.com; Vivi, Rodrigo <rodrigo.vivi@intel.com>; tursulin@ursulin.net; airlied@gmail.com; daniel@ffwll.ch Cc: intel-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org; linux-kernel@vger.kernel.org; Thorsten Blum <thorsten.blum@toblux.com> Subject: [PATCH v2] drm/i915: Explicitly cast divisor and use div_u64() > > 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 > > Use the preferred div_u64() function instead of the do_div() macro and > remove the now unnecessary local variable tmp. > > Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com> > --- > Changes in v2: > - Use div_u64() instead of do_div() after feedback from Ville Syrjälä > - Link to v1: https://lore.kernel.org/linux-kernel/20240710074650.419902-2-thorsten.blum@toblux.com/ > --- > drivers/gpu/drm/i915/i915_perf.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c > index 0b1cd4c7a525..f65fbe13ab59 100644 > --- a/drivers/gpu/drm/i915/i915_perf.c > +++ b/drivers/gpu/drm/i915/i915_perf.c > @@ -4096,15 +4096,13 @@ static int read_properties_unlocked(struct i915_perf *perf, > oa_period = oa_exponent_to_ns(perf, value); > > /* This check is primarily to ensure that oa_period <= > - * UINT32_MAX (before passing to do_div which only > + * UINT32_MAX (before passing it to div_u64 which only > * accepts a u32 denominator), but we can also skip > * checking anything < 1Hz which implicitly can't be > * limited via an integer oa_max_sample_rate. > */ > if (oa_period <= NSEC_PER_SEC) { > - u64 tmp = NSEC_PER_SEC; > - do_div(tmp, oa_period); > - oa_freq_hz = tmp; > + oa_freq_hz = div_u64(NSEC_PER_SEC, (u32)oa_period); > } else > oa_freq_hz = 0; Non-blocking suggestion: this looks like it can be inlined. And if the inline route is taken, it might be best to invert the conditional check like such: oa_freq_hz = oa_period > NSEC_PER_SEC ? 0 : div_u64(NSEC_PER_SEC, (u32)oa_period); I think this is just a matter of preference, though. The explicit if-else block is definitely clearer. Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com> -Jonathan Cavitt > > -- > 2.45.2 > >
Hi Thorsten, > > /* This check is primarily to ensure that oa_period <= > > - * UINT32_MAX (before passing to do_div which only > > + * UINT32_MAX (before passing it to div_u64 which only > > * accepts a u32 denominator), but we can also skip > > * checking anything < 1Hz which implicitly can't be > > * limited via an integer oa_max_sample_rate. > > */ > > if (oa_period <= NSEC_PER_SEC) { > > - u64 tmp = NSEC_PER_SEC; > > - do_div(tmp, oa_period); > > - oa_freq_hz = tmp; > > + oa_freq_hz = div_u64(NSEC_PER_SEC, (u32)oa_period); > > } else > > oa_freq_hz = 0; > > Non-blocking suggestion: this looks like it can be inlined. And if the > inline route is taken, it might be best to invert the conditional check > like such: > > oa_freq_hz = oa_period > NSEC_PER_SEC ? 0 : > div_u64(NSEC_PER_SEC, (u32)oa_period); > > I think this is just a matter of preference, though. The explicit if-else > block is definitely clearer. It's also stylistically wrong given that now the if/else don't need the brackets anymore, triggering a checkpatch error. Thorsten do you mind resending it either following Jonathan's suggestion (my favourite, as well) or fix the bracket issue following the kernel style. Andi
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c index 0b1cd4c7a525..f65fbe13ab59 100644 --- a/drivers/gpu/drm/i915/i915_perf.c +++ b/drivers/gpu/drm/i915/i915_perf.c @@ -4096,15 +4096,13 @@ static int read_properties_unlocked(struct i915_perf *perf, oa_period = oa_exponent_to_ns(perf, value); /* This check is primarily to ensure that oa_period <= - * UINT32_MAX (before passing to do_div which only + * UINT32_MAX (before passing it to div_u64 which only * accepts a u32 denominator), but we can also skip * checking anything < 1Hz which implicitly can't be * limited via an integer oa_max_sample_rate. */ if (oa_period <= NSEC_PER_SEC) { - u64 tmp = NSEC_PER_SEC; - do_div(tmp, oa_period); - oa_freq_hz = tmp; + oa_freq_hz = div_u64(NSEC_PER_SEC, (u32)oa_period); } 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 Use the preferred div_u64() function instead of the do_div() macro and remove the now unnecessary local variable tmp. Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com> --- Changes in v2: - Use div_u64() instead of do_div() after feedback from Ville Syrjälä - Link to v1: https://lore.kernel.org/linux-kernel/20240710074650.419902-2-thorsten.blum@toblux.com/ --- drivers/gpu/drm/i915/i915_perf.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)