From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Guru Das Srinagesh <gurus@codeaurora.org>,
linux-pwm@vger.kernel.org,
Thierry Reding <thierry.reding@gmail.com>,
Subbaraman Narayanamurthy <subbaram@codeaurora.org>,
linux-kernel@vger.kernel.org, Kamil Debski <kamil@wypas.org>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
Jean Delvare <jdelvare@suse.com>,
Liam Girdwood <lgirdwood@gmail.com>,
Mark Brown <broonie@kernel.org>,
linux-hwmon@vger.kernel.org
Subject: Re: [PATCH v7 03/13] hwmon: pwm-fan: Use 64-bit division macros for period and duty cycle
Date: Tue, 10 Mar 2020 13:08:14 +0100 [thread overview]
Message-ID: <20200310120814.4kjxmii3c7zxw55y@pengutronix.de> (raw)
In-Reply-To: <20200309214822.GA19773@roeck-us.net>
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/ |
next prev parent reply other threads:[~2020-03-10 12:08 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1583782035.git.gurus@codeaurora.org>
2020-03-09 19:35 ` [PATCH v7 03/13] hwmon: pwm-fan: Use 64-bit division macros for period and duty cycle Guru Das Srinagesh
2020-03-09 21:48 ` Guenter Roeck
2020-03-10 12:08 ` Uwe Kleine-König [this message]
2020-03-10 15:05 ` Guenter Roeck
2020-03-10 22:24 ` Guru Das Srinagesh
2020-03-10 22:57 ` Guenter Roeck
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