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Wed, 22 Jul 2026 09:03:42 -0700 (PDT) Date: Wed, 22 Jul 2026 21:33:33 +0530 From: Mohamad Raizudeen To: Joshua Crofts Cc: jic23@kernel.org, dlechner@baylibre.com, andy@kernel.org, nuno.sa@analog.com, gregkh@linuxfoundation.org, skhan@linuxfoundation.org, me@brighamcampbell.com, jkoolstra@xs4all.nl, linux-iio@vger.kernel.org, linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, Andy Shevchenko Subject: Re: [PATCH v2] staging: iio: frequency: ad9832/ad9834: add comment explaining do_div usage Message-ID: References: <20260630032322.5805-1-raizudeen.kerneldev@gmail.com> <20260722082227.18768-1-raizudeen.kerneldev@gmail.com> <20260722104617.000050fa@gmail.com> Precedence: bulk X-Mailing-List: linux-iio@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260722104617.000050fa@gmail.com> On Wed, Jul 22, 2026 at 10:46:17AM +0200, Joshua Crofts wrote: > On Wed, 22 Jul 2026 13:52:27 +0530 > Mohamad Raizudeen wrote: > > Previous attempts to change do_div() to div64_ul() were rejected because > > mclk will always fit within 32 bits for this hardware, making do_div() > > safe to use. > > > > However, Coccinelle continues to flag this as a false positive. To > > prevent future developers from submitting unnecessary fixes, add a > > comment explaining why do_div() is intentionally kept. > > > > Suggested-by: Andy Shevchenko > > Signed-off-by: Mohamad Raizudeen > > --- > > Please don't send a new version as a reply to the previous version, > as it can break tooling such as b4 for patch review. > > As for the comment, I think it's good, however I'm not sure whether > this should be split into two patches, given that this is a small > change. Andy, what do you think? > > > diff --git a/drivers/staging/iio/frequency/ad9832.c b/drivers/staging/iio/frequency/ad9832.c > > index 60c33e10c46f..6d046e9121e2 100644 > > --- a/drivers/staging/iio/frequency/ad9832.c > > +++ b/drivers/staging/iio/frequency/ad9832.c > > @@ -118,6 +118,13 @@ static unsigned long ad9832_calc_freqreg(unsigned long mclk, unsigned long fout) > > { > > u64 freqreg = (u64)fout << AD9832_FREQ_BITS; > > > > + /* > > + * mclk is an unsigned long, which triggers a Coccinelle false positive > > + * warning about using do_div() for 64-by-32 division. However, mclk > > + * for this hardware will always fit within 32 bits, so do_div() is > > + * safe to use here. > > + */ > > + > > Unnecessary blank line here, you want to couple the comment with the > line that it's describing. > > > do_div(freqreg, mclk); > > return freqreg; > > } > > diff --git a/drivers/staging/iio/frequency/ad9834.c b/drivers/staging/iio/frequency/ad9834.c > > index 33dfd723923c..8722f3a01cde 100644 > > --- a/drivers/staging/iio/frequency/ad9834.c > > +++ b/drivers/staging/iio/frequency/ad9834.c > > @@ -103,6 +103,13 @@ static unsigned int ad9834_calc_freqreg(unsigned long mclk, unsigned long fout) > > { > > unsigned long long freqreg = (u64)fout * (u64)BIT(AD9834_FREQ_BITS); > > > > + /* > > + * mclk is an unsigned long, which triggers a Coccinelle false positive > > + * warning about using do_div() for 64-by-32 division. However, mclk > > + * for this hardware will always fit within 32 bits, so do_div() is > > + * safe to use here. > > + */ > > + > > Ditto. > > > do_div(freqreg, mclk); > > return freqreg; > > } > > > > -- > Kind regards, > Joshua Crofts Hi Joshua, Thanks you for reviewing the patch and for the clarifications. I understood and will make sure v3 is sent as a new and separate email thread without in-reply-to header so i doesn't break b4. Sure, I will remove the unnecessary blank line. I will hold off sending v3 until I hear from Andy regarding whether this should be split into two patches or kept as one. Thanks & regards, Mohamad Raizudeen