| Message ID | 3dc95ebc6539066cc58bc44c0e6e53ac979fe9a9.1584667964.git.gurus@codeaurora.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v11,01/12] drm/i915: Use 64-bit division macro | expand |
On Fri, Mar 20, 2020 at 2:41 AM Guru Das Srinagesh <gurus@codeaurora.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 UINT_MAX will cause the quotient to be zero, so return 0 in that > case to efficiently skip the division. > > Cc: Alexander Shiyan <shc_work@mail.ru> > Cc: Arnd Bergmann <arnd@arndb.de> > > Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org> Reviewed-by: Arnd Bergmann <arnd@arndb.de>
On Fri, Mar 20, 2020 at 06:11:42PM +0100, Arnd Bergmann wrote: > On Fri, Mar 20, 2020 at 2:41 AM Guru Das Srinagesh <gurus@codeaurora.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 UINT_MAX will cause the quotient to be zero, so return 0 in that > > case to efficiently skip the division. > > > > Cc: Alexander Shiyan <shc_work@mail.ru> > > Cc: Arnd Bergmann <arnd@arndb.de> > > > > Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org> > > Reviewed-by: Arnd Bergmann <arnd@arndb.de> The stated aim of adding the if condition is to determine when the division operation may be skipped as the quotient would be zero anyway [1]. That said, I think the current if condition is incorrect. The quotient would be zero only when the denominator of the division exceeds (v * 0xf) and not UINT_MAX. In fact, UINT_MAX has no bearing on whether the quotient becomes zero or not. Therefore, the correct if condition should be: - return DIV_ROUND_CLOSEST(v * 0xf, pwm->args.period); + if ((u32)pwm->args.period > (v * 0xf)) + return 0; + + return DIV_ROUND_CLOSEST(v * 0xf, (u32)pwm->args.period); What do you think? [1] https://www.spinics.net/lists/linux-pwm/msg11908.html Thank you. Guru Das.
diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c index 924d39a..f34f1f3 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 (pwm->args.period > UINT_MAX) + 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)
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 UINT_MAX will cause the quotient to be zero, so return 0 in that case to efficiently skip the division. Cc: Alexander Shiyan <shc_work@mail.ru> Cc: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org> --- drivers/pwm/pwm-clps711x.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)