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Date: Thu, 23 Apr 2020 11:30:19 +0200 From: Geert Uytterhoeven <geert@...ux-m68k.org> To: Guru Das Srinagesh <gurus@...eaurora.org> Cc: Linux PWM List <linux-pwm@...r.kernel.org>, Thierry Reding <thierry.reding@...il.com>, Uwe Kleine-König <u.kleine-koenig@...gutronix.de>, Subbaraman Narayanamurthy <subbaram@...eaurora.org>, David Collins <collinsd@...eaurora.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Alexander Shiyan <shc_work@...l.ru>, Arnd Bergmann <arnd@...db.de> Subject: Re: [PATCH v13 04/11] pwm: clps711x: Cast period to u32 before use as divisor On Wed, Apr 22, 2020 at 5:00 AM Guru Das Srinagesh <gurus@...eaurora.org> wrote: > Since the PWM framework is switching struct pwm_args.period's datatype > to u64, prepare for this transition by typecasting it to u32. > > Also, since the dividend is still a 32-bit number, any divisor greater > than the numerator will cause the quotient to be zero, so return 0 in > that case to efficiently skip the division. > > Cc: Alexander Shiyan <shc_work@...l.ru> > Cc: Arnd Bergmann <arnd@...db.de> > > Signed-off-by: Guru Das Srinagesh <gurus@...eaurora.org> > --- > drivers/pwm/pwm-clps711x.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c > index 924d39a..0d368ac 100644 > --- a/drivers/pwm/pwm-clps711x.c > +++ b/drivers/pwm/pwm-clps711x.c > @@ -43,7 +43,10 @@ static void clps711x_pwm_update_val(struct clps711x_chip *priv, u32 n, u32 v) > static unsigned int clps711x_get_duty(struct pwm_device *pwm, unsigned int v) > { > /* Duty cycle 0..15 max */ > - return DIV_ROUND_CLOSEST(v * 0xf, pwm->args.period); > + if ((u32)pwm->args.period > (v * 0xf)) Shouldn't the cast be removed from the expression above? Else a period larger than or equal to 2^32 may be accepted, but truncated silently. And even cause a division by zero error. > + return 0; > + > + return DIV_ROUND_CLOSEST(v * 0xf, (u32)pwm->args.period); > } > > static int clps711x_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm) Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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