| Message ID | 587f9ccae68ad7e1ce97fa8da6037292af1a5095.1584473399.git.gurus@codeaurora.org |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | [v9,01/11] drm/i915: Use 64-bit division macro | expand |
On Tue, Mar 17, 2020 at 9:05 PM 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 using DIV64_U64_ROUND_CLOSEST to > handle a 64-bit divisor. > > 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 | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c > index 924d39a..ba9500a 100644 > --- a/drivers/pwm/pwm-clps711x.c > +++ b/drivers/pwm/pwm-clps711x.c > @@ -43,7 +43,7 @@ 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); > + return DIV64_U64_ROUND_CLOSEST(v * 0xf, pwm->args.period); > } Is it actually going to exceed U32_MAX? If not, a type cast may be more appropriate here than the expensive 64-bit division. Arnd
On Tue, Mar 17, 2020 at 11:22:06PM +0100, Arnd Bergmann wrote: > > diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c > > index 924d39a..ba9500a 100644 > > --- a/drivers/pwm/pwm-clps711x.c > > +++ b/drivers/pwm/pwm-clps711x.c > > @@ -43,7 +43,7 @@ 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); > > + return DIV64_U64_ROUND_CLOSEST(v * 0xf, pwm->args.period); > > } > > Is it actually going to exceed U32_MAX? If not, a type cast may be > more appropriate here than the expensive 64-bit division. With the final change in this patch series, the framework will support periods that exceed U32_MAX. My concern is that using a typecast would mean that in those cases, this driver will not support > U32_MAX values. Using DIV64_U64_ROUND_CLOSEST makes the driver future proof and able to handle > U32_MAX values correctly. What do you think? Thank you. Guru Das.
On Wed, Mar 18, 2020 at 12:30 AM Guru Das Srinagesh <gurus@codeaurora.org> wrote: > > On Tue, Mar 17, 2020 at 11:22:06PM +0100, Arnd Bergmann wrote: > > > diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c > > > index 924d39a..ba9500a 100644 > > > --- a/drivers/pwm/pwm-clps711x.c > > > +++ b/drivers/pwm/pwm-clps711x.c > > > @@ -43,7 +43,7 @@ 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); > > > + return DIV64_U64_ROUND_CLOSEST(v * 0xf, pwm->args.period); > > > } > > > > Is it actually going to exceed U32_MAX? If not, a type cast may be > > more appropriate here than the expensive 64-bit division. > > With the final change in this patch series, the framework will support > periods that exceed U32_MAX. My concern is that using a typecast would > mean that in those cases, this driver will not support > U32_MAX values. > Using DIV64_U64_ROUND_CLOSEST makes the driver future proof and able to > handle > U32_MAX values correctly. What do you think? Ah, so if the period can actually be larger than U32_MAX, you need to handle that case. However, I see that the divident in this code (v * 0xf) is still a 32-bit number, so a correct and efficient implementation could be if (pwm->args.period > (UINT_MAX / 0xf)) return 0; return DIV_ROUND_CLOSEST(v * 0xf, (u32)pwm->args.period); Arnd
On Wed, Mar 18, 2020 at 10:49:34AM +0100, Arnd Bergmann wrote: > On Wed, Mar 18, 2020 at 12:30 AM Guru Das Srinagesh > <gurus@codeaurora.org> wrote: > > > > On Tue, Mar 17, 2020 at 11:22:06PM +0100, Arnd Bergmann wrote: > > > > diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c > > > > index 924d39a..ba9500a 100644 > > > > --- a/drivers/pwm/pwm-clps711x.c > > > > +++ b/drivers/pwm/pwm-clps711x.c > > > > @@ -43,7 +43,7 @@ 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); > > > > + return DIV64_U64_ROUND_CLOSEST(v * 0xf, pwm->args.period); > > > > } > > > > > > Is it actually going to exceed U32_MAX? If not, a type cast may be > > > more appropriate here than the expensive 64-bit division. > > > > With the final change in this patch series, the framework will support > > periods that exceed U32_MAX. My concern is that using a typecast would > > mean that in those cases, this driver will not support > U32_MAX values. > > Using DIV64_U64_ROUND_CLOSEST makes the driver future proof and able to > > handle > U32_MAX values correctly. What do you think? > > Ah, so if the period can actually be larger than U32_MAX, you need to > handle that case. However, I see that the divident in this code (v * 0xf) > is still a 32-bit number, so a correct and efficient implementation could be > > if (pwm->args.period > (UINT_MAX / 0xf)) Shouldn't the if condition be the following? Or am I missing something here? if (pwm->args.period > (UINT_MAX / (v * 0xf))) ^^^^^^^^^ > return 0; > return DIV_ROUND_CLOSEST(v * 0xf, (u32)pwm->args.period); Thank you. Guru Das.
On Wed, Mar 18, 2020 at 6:00 PM Guru Das Srinagesh <gurus@codeaurora.org> wrote: > > On Wed, Mar 18, 2020 at 10:49:34AM +0100, Arnd Bergmann wrote: > > On Wed, Mar 18, 2020 at 12:30 AM Guru Das Srinagesh > > <gurus@codeaurora.org> wrote: > > > > > > On Tue, Mar 17, 2020 at 11:22:06PM +0100, Arnd Bergmann wrote: > > > > > diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c > > > > > index 924d39a..ba9500a 100644 > > > > > --- a/drivers/pwm/pwm-clps711x.c > > > > > +++ b/drivers/pwm/pwm-clps711x.c > > > > > @@ -43,7 +43,7 @@ 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); > > > > > + return DIV64_U64_ROUND_CLOSEST(v * 0xf, pwm->args.period); > > > > > } > > > > > > > > Is it actually going to exceed U32_MAX? If not, a type cast may be > > > > more appropriate here than the expensive 64-bit division. > > > > > > With the final change in this patch series, the framework will support > > > periods that exceed U32_MAX. My concern is that using a typecast would > > > mean that in those cases, this driver will not support > U32_MAX values. > > > Using DIV64_U64_ROUND_CLOSEST makes the driver future proof and able to > > > handle > U32_MAX values correctly. What do you think? > > > > Ah, so if the period can actually be larger than U32_MAX, you need to > > handle that case. However, I see that the divident in this code (v * 0xf) > > is still a 32-bit number, so a correct and efficient implementation could be > > > > if (pwm->args.period > (UINT_MAX / 0xf)) > > Shouldn't the if condition be the following? Or am I missing > something here? > > if (pwm->args.period > (UINT_MAX / (v * 0xf))) > ^^^^^^^^^ That would require performing a division, which is an external function call on ARMv4. My version just checks for an upper bound and completely avoids the division. You could also just check for ">UINT_MAX" if you find that clearer. Arnd
On Wed, Mar 18, 2020 at 08:38:29PM +0100, Arnd Bergmann wrote: > On Wed, Mar 18, 2020 at 6:00 PM Guru Das Srinagesh <gurus@codeaurora.org> wrote: > > > > On Wed, Mar 18, 2020 at 10:49:34AM +0100, Arnd Bergmann wrote: > > > On Wed, Mar 18, 2020 at 12:30 AM Guru Das Srinagesh > > > <gurus@codeaurora.org> wrote: > > > > > > > > On Tue, Mar 17, 2020 at 11:22:06PM +0100, Arnd Bergmann wrote: > > > > > > diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c > > > > > > index 924d39a..ba9500a 100644 > > > > > > --- a/drivers/pwm/pwm-clps711x.c > > > > > > +++ b/drivers/pwm/pwm-clps711x.c > > > > > > @@ -43,7 +43,7 @@ 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); > > > > > > + return DIV64_U64_ROUND_CLOSEST(v * 0xf, pwm->args.period); > > > > > > } > > > > > > > > > > Is it actually going to exceed U32_MAX? If not, a type cast may be > > > > > more appropriate here than the expensive 64-bit division. > > > > > > > > With the final change in this patch series, the framework will support > > > > periods that exceed U32_MAX. My concern is that using a typecast would > > > > mean that in those cases, this driver will not support > U32_MAX values. > > > > Using DIV64_U64_ROUND_CLOSEST makes the driver future proof and able to > > > > handle > U32_MAX values correctly. What do you think? > > > > > > Ah, so if the period can actually be larger than U32_MAX, you need to > > > handle that case. However, I see that the divident in this code (v * 0xf) > > > is still a 32-bit number, so a correct and efficient implementation could be > > > > > > if (pwm->args.period > (UINT_MAX / 0xf)) > > > > Shouldn't the if condition be the following? Or am I missing > > something here? > > > > if (pwm->args.period > (UINT_MAX / (v * 0xf))) > > ^^^^^^^^^ > > That would require performing a division, which is an external function > call on ARMv4. My version just checks for an upper bound and completely > avoids the division. You could also just check for ">UINT_MAX" if you > find that clearer. Thanks, have checked for UINT_MAX in v10 of my patchset that I just uploaded. Could you please review it? Thank you. Guru Das.
diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c index 924d39a..ba9500a 100644 --- a/drivers/pwm/pwm-clps711x.c +++ b/drivers/pwm/pwm-clps711x.c @@ -43,7 +43,7 @@ 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); + return DIV64_U64_ROUND_CLOSEST(v * 0xf, 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 using DIV64_U64_ROUND_CLOSEST to handle a 64-bit divisor. 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 | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)