From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Baruch Siach <baruch@tkos.co.il>
Cc: "Thierry Reding" <thierry.reding@gmail.com>,
"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
"Lee Jones" <lee.jones@linaro.org>,
"Linus Walleij" <linus.walleij@linaro.org>,
"Bartosz Golaszewski" <bgolaszewski@baylibre.com>,
"Rob Herring" <robh+dt@kernel.org>,
"Andrew Lunn" <andrew@lunn.ch>,
"Gregory Clement" <gregory.clement@bootlin.com>,
"Sebastian Hesselbarth" <sebastian.hesselbarth@gmail.com>,
"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
"Chris Packham" <chris.packham@alliedtelesis.co.nz>,
"Sascha Hauer" <s.hauer@pengutronix.de>,
"Ralph Sennhauser" <ralph.sennhauser@gmail.com>,
linux-pwm@vger.kernel.org, linux-gpio@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org
Subject: Re: [PATCH v5 1/4] gpio: mvebu: fix pwm get_state period calculation
Date: Tue, 5 Jan 2021 12:49:18 +0000 [thread overview]
Message-ID: <20210105124917.GC1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <0cd077886d37699bdf0a20295fd8ee422e5285b5.1609849176.git.baruch@tkos.co.il>
On Tue, Jan 05, 2021 at 02:42:28PM +0200, Baruch Siach wrote:
> The period is the sum of on and off values.
>
> Reported-by: Russell King <linux@armlinux.org.uk>
> Fixes: 757642f9a584e ("gpio: mvebu: Add limited PWM support")
> Signed-off-by: Baruch Siach <baruch@tkos.co.il>
> ---
> drivers/gpio/gpio-mvebu.c | 16 ++++++----------
> 1 file changed, 6 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
> index 672681a976f5..ac7cb6d3702e 100644
> --- a/drivers/gpio/gpio-mvebu.c
> +++ b/drivers/gpio/gpio-mvebu.c
> @@ -679,17 +679,13 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
> regmap_read(mvpwm->regs, mvebu_pwmreg_blink_off_duration(mvpwm), &u);
> val = (unsigned long long) u * NSEC_PER_SEC;
> do_div(val, mvpwm->clk_rate);
> - if (val < state->duty_cycle) {
> + val += state->duty_cycle;
> + if (val > UINT_MAX)
> + state->period = UINT_MAX;
> + else if (val)
> + state->period = val;
> + else
> state->period = 1;
Are you sure this is the correct solution? Aren't you introducing
rounding errors?
The hardware will count to (on + off) clock ticks, so the right way
to convert that is to add the two together and then convert to
nanoseconds, which may result in a single rounding error. If you
convert each individually to nanoseconds, then you can end up with
two sets of rounding errors.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
WARNING: multiple messages have this Message-ID (diff)
From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Baruch Siach <baruch@tkos.co.il>
Cc: "Andrew Lunn" <andrew@lunn.ch>,
"Sascha Hauer" <s.hauer@pengutronix.de>,
linux-pwm@vger.kernel.org,
"Linus Walleij" <linus.walleij@linaro.org>,
"Chris Packham" <chris.packham@alliedtelesis.co.nz>,
linux-gpio@vger.kernel.org, "Rob Herring" <robh+dt@kernel.org>,
"Bartosz Golaszewski" <bgolaszewski@baylibre.com>,
devicetree@vger.kernel.org,
"Thierry Reding" <thierry.reding@gmail.com>,
"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
"Ralph Sennhauser" <ralph.sennhauser@gmail.com>,
"Lee Jones" <lee.jones@linaro.org>,
"Gregory Clement" <gregory.clement@bootlin.com>,
linux-arm-kernel@lists.infradead.org,
"Sebastian Hesselbarth" <sebastian.hesselbarth@gmail.com>
Subject: Re: [PATCH v5 1/4] gpio: mvebu: fix pwm get_state period calculation
Date: Tue, 5 Jan 2021 12:49:18 +0000 [thread overview]
Message-ID: <20210105124917.GC1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <0cd077886d37699bdf0a20295fd8ee422e5285b5.1609849176.git.baruch@tkos.co.il>
On Tue, Jan 05, 2021 at 02:42:28PM +0200, Baruch Siach wrote:
> The period is the sum of on and off values.
>
> Reported-by: Russell King <linux@armlinux.org.uk>
> Fixes: 757642f9a584e ("gpio: mvebu: Add limited PWM support")
> Signed-off-by: Baruch Siach <baruch@tkos.co.il>
> ---
> drivers/gpio/gpio-mvebu.c | 16 ++++++----------
> 1 file changed, 6 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
> index 672681a976f5..ac7cb6d3702e 100644
> --- a/drivers/gpio/gpio-mvebu.c
> +++ b/drivers/gpio/gpio-mvebu.c
> @@ -679,17 +679,13 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
> regmap_read(mvpwm->regs, mvebu_pwmreg_blink_off_duration(mvpwm), &u);
> val = (unsigned long long) u * NSEC_PER_SEC;
> do_div(val, mvpwm->clk_rate);
> - if (val < state->duty_cycle) {
> + val += state->duty_cycle;
> + if (val > UINT_MAX)
> + state->period = UINT_MAX;
> + else if (val)
> + state->period = val;
> + else
> state->period = 1;
Are you sure this is the correct solution? Aren't you introducing
rounding errors?
The hardware will count to (on + off) clock ticks, so the right way
to convert that is to add the two together and then convert to
nanoseconds, which may result in a single rounding error. If you
convert each individually to nanoseconds, then you can end up with
two sets of rounding errors.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-01-05 12:50 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-05 12:42 [PATCH v5 0/4] gpio: mvebu: Armada 8K/7K PWM support Baruch Siach
2021-01-05 12:42 ` Baruch Siach
2021-01-05 12:42 ` [PATCH v5 1/4] gpio: mvebu: fix pwm get_state period calculation Baruch Siach
2021-01-05 12:42 ` Baruch Siach
2021-01-05 12:49 ` Russell King - ARM Linux admin [this message]
2021-01-05 12:49 ` Russell King - ARM Linux admin
2021-01-05 12:42 ` [PATCH v5 2/4] gpio: mvebu: add pwm support for Armada 8K/7K Baruch Siach
2021-01-05 12:42 ` Baruch Siach
2021-01-05 12:42 ` [PATCH v5 3/4] arm64: dts: armada: add pwm offsets for ap/cp gpios Baruch Siach
2021-01-05 12:42 ` Baruch Siach
2021-01-05 12:42 ` [PATCH v5 4/4] dt-bindings: ap806: document gpio marvell,pwm-offset property Baruch Siach
2021-01-05 12:42 ` [PATCH v5 4/4] dt-bindings: ap806: document gpio marvell, pwm-offset property Baruch Siach
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