[PATCH v7 03/13] hwmon: pwm-fan: Use 64-bit division macros for period and duty cycle

[PATCH v7 03/13] hwmon: pwm-fan: Use 64-bit division macros for period and duty cycle

[Guru Das Srinagesh]

Because period and duty cycle are defined in the PWM framework structs
as ints with units of nanoseconds, the maximum time duration that can be
set is limited to ~2.147 seconds. Redefining them as u64 values will
enable larger time durations to be set.

As a first step, prepare drivers to handle the switch to u64 period and
duty_cycle by replacing division operations involving pwm period and duty cycle
with their 64-bit equivalents as appropriate. The actual switch to u64 period
and duty_cycle follows as a separate patch.

Where the dividend is 64-bit but the divisor is 32-bit, use *_ULL
macros:
- DIV_ROUND_UP_ULL
- DIV_ROUND_CLOSEST_ULL
- div_u64

Where the divisor is 64-bit (dividend may be 32-bit or 64-bit), use
DIV64_* macros:
- DIV64_U64_ROUND_CLOSEST
- div64_u64

Cc: Kamil Debski <kamil@wypas.org>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Jean Delvare <jdelvare@suse.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: linux-hwmon@vger.kernel.org

Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>
---
 drivers/hwmon/pwm-fan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
index 42ffd2e..283423a 100644
--- a/drivers/hwmon/pwm-fan.c
+++ b/drivers/hwmon/pwm-fan.c
@@ -437,7 +437,7 @@ static int pwm_fan_resume(struct device *dev)
 		return 0;
 
 	pwm_get_args(ctx->pwm, &pargs);
-	duty = DIV_ROUND_UP(ctx->pwm_value * (pargs.period - 1), MAX_PWM);
+	duty = DIV_ROUND_UP_ULL(ctx->pwm_value * (pargs.period - 1), MAX_PWM);
 	ret = pwm_config(ctx->pwm, duty, pargs.period);
 	if (ret)
 		return ret;
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH v7 03/13] hwmon: pwm-fan: Use 64-bit division macros for period and duty cycle

[Guenter Roeck]

On Mon, Mar 09, 2020 at 12:35:06PM -0700, Guru Das Srinagesh wrote:
> Because period and duty cycle are defined in the PWM framework structs
> as ints with units of nanoseconds, the maximum time duration that can be
> set is limited to ~2.147 seconds. Redefining them as u64 values will
> enable larger time durations to be set.
> 
> As a first step, prepare drivers to handle the switch to u64 period and
> duty_cycle by replacing division operations involving pwm period and duty cycle
> with their 64-bit equivalents as appropriate. The actual switch to u64 period
> and duty_cycle follows as a separate patch.
> 
> Where the dividend is 64-bit but the divisor is 32-bit, use *_ULL
> macros:
> - DIV_ROUND_UP_ULL
> - DIV_ROUND_CLOSEST_ULL
> - div_u64
> 
> Where the divisor is 64-bit (dividend may be 32-bit or 64-bit), use
> DIV64_* macros:
> - DIV64_U64_ROUND_CLOSEST
> - div64_u64
> 
There is no explanation why this is necessary. What is the use case ?
It is hard to imagine a real-world use case with a duty cycle of more
than 2 seconds.

Guenter

Re: [PATCH v7 03/13] hwmon: pwm-fan: Use 64-bit division macros for period and duty cycle

[Uwe Kleine-König]

Hello Guenter,

On Mon, Mar 09, 2020 at 02:48:22PM -0700, Guenter Roeck wrote:
> On Mon, Mar 09, 2020 at 12:35:06PM -0700, Guru Das Srinagesh wrote:
> > Because period and duty cycle are defined in the PWM framework structs
> > as ints with units of nanoseconds, the maximum time duration that can be
> > set is limited to ~2.147 seconds. Redefining them as u64 values will
> > enable larger time durations to be set.
> > 
> > As a first step, prepare drivers to handle the switch to u64 period and
> > duty_cycle by replacing division operations involving pwm period and duty cycle
> > with their 64-bit equivalents as appropriate. The actual switch to u64 period
> > and duty_cycle follows as a separate patch.
> > 
> > Where the dividend is 64-bit but the divisor is 32-bit, use *_ULL
> > macros:
> > - DIV_ROUND_UP_ULL
> > - DIV_ROUND_CLOSEST_ULL
> > - div_u64
> > 
> > Where the divisor is 64-bit (dividend may be 32-bit or 64-bit), use
> > DIV64_* macros:
> > - DIV64_U64_ROUND_CLOSEST
> > - div64_u64
>
> There is no explanation why this is necessary. What is the use case ?
> It is hard to imagine a real-world use case with a duty cycle of more
> than 2 seconds.

When my Laptop is in suspend there is an LED that blinks with a period
of approximately 5 seconds. (To be fair, the brightness is more a sinus
than a rectangle, but still.)

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

Re: [PATCH v7 03/13] hwmon: pwm-fan: Use 64-bit division macros for period and duty cycle

[Guenter Roeck]

On 3/10/20 5:08 AM, Uwe Kleine-König wrote:
> Hello Guenter,
> 
> On Mon, Mar 09, 2020 at 02:48:22PM -0700, Guenter Roeck wrote:
>> On Mon, Mar 09, 2020 at 12:35:06PM -0700, Guru Das Srinagesh wrote:
>>> Because period and duty cycle are defined in the PWM framework structs
>>> as ints with units of nanoseconds, the maximum time duration that can be
>>> set is limited to ~2.147 seconds. Redefining them as u64 values will
>>> enable larger time durations to be set.
>>>
>>> As a first step, prepare drivers to handle the switch to u64 period and
>>> duty_cycle by replacing division operations involving pwm period and duty cycle
>>> with their 64-bit equivalents as appropriate. The actual switch to u64 period
>>> and duty_cycle follows as a separate patch.
>>>
>>> Where the dividend is 64-bit but the divisor is 32-bit, use *_ULL
>>> macros:
>>> - DIV_ROUND_UP_ULL
>>> - DIV_ROUND_CLOSEST_ULL
>>> - div_u64
>>>
>>> Where the divisor is 64-bit (dividend may be 32-bit or 64-bit), use
>>> DIV64_* macros:
>>> - DIV64_U64_ROUND_CLOSEST
>>> - div64_u64
>>
>> There is no explanation why this is necessary. What is the use case ?
>> It is hard to imagine a real-world use case with a duty cycle of more
>> than 2 seconds.
> 
> When my Laptop is in suspend there is an LED that blinks with a period
> of approximately 5 seconds. (To be fair, the brightness is more a sinus
> than a rectangle, but still.)
> 

I don't see support in the LED subsystem to utilize the PWM framework directly
for blinking. Plus, you say yourself that it isn't a _real_ use case, just a
theoretic one.

Either case, the reason / use case for this series should be explained
in the summary patch. That is what it is for. That case is not made.

Guenter

Re: [PATCH v7 03/13] hwmon: pwm-fan: Use 64-bit division macros for period and duty cycle

[Guru Das Srinagesh]

On Tue, Mar 10, 2020 at 08:05:58AM -0700, Guenter Roeck wrote:
> I don't see support in the LED subsystem to utilize the PWM framework directly
> for blinking. Plus, you say yourself that it isn't a _real_ use case, just a
> theoretic one.

An example use case is a mobile phone OEM that wishes to set a period of
5 seconds or more for, say, a low battery slow blinking indication - currently
this is not possible. The PWM framework not having direct support for
blinking should not be a concern if the PWM peripheral being controlled
supports it via register writes.

> Either case, the reason / use case for this series should be explained
> in the summary patch. That is what it is for. That case is not made.

Will upload a new patchset adding more details in the summary patch.

Thank you.

Guru Das.

Re: [PATCH v7 03/13] hwmon: pwm-fan: Use 64-bit division macros for period and duty cycle

[Guenter Roeck]

On 3/10/20 3:24 PM, Guru Das Srinagesh wrote:
> On Tue, Mar 10, 2020 at 08:05:58AM -0700, Guenter Roeck wrote:
>> I don't see support in the LED subsystem to utilize the PWM framework directly
>> for blinking. Plus, you say yourself that it isn't a _real_ use case, just a
>> theoretic one.
> 
> An example use case is a mobile phone OEM that wishes to set a period of
> 5 seconds or more for, say, a low battery slow blinking indication - currently
> this is not possible. The PWM framework not having direct support for
> blinking should not be a concern if the PWM peripheral being controlled
> supports it via register writes.
> 
>> Either case, the reason / use case for this series should be explained
>> in the summary patch. That is what it is for. That case is not made.
> 
> Will upload a new patchset adding more details in the summary patch.
> 

Well, let's assume that this is a real use case.

Please also add information about alternatives considered, such as keeping
the second-part of the period in a separate variable.

Guenter