From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de> To: Claudiu Beznea <claudiu.beznea@microchip.com>, Thierry Reding <thierry.reding@gmail.com>, Lee Jones <lee.jones@linaro.org> Cc: linux-pwm@vger.kernel.org, Alexandre Belloni <alexandre.belloni@bootlin.com>, Nicolas Ferre <nicolas.ferre@microchip.com>, Ludovic Desroches <ludovic.desroches@microchip.com>, kernel@pengutronix.de, linux-arm-kernel@lists.infradead.org Subject: Re: overflow and wrong timeout errors in pwm-atmel Date: Wed, 21 Apr 2021 15:48:25 +0200 [thread overview] Message-ID: <20210421134825.powx5tvqvce32fho@pengutronix.de> (raw) In-Reply-To: <20210421110336.bd5s6e2kjxqilddi@pengutronix.de> [-- Attachment #1: Type: text/plain, Size: 1628 bytes --] On Wed, Apr 21, 2021 at 01:03:36PM +0200, Uwe Kleine-König wrote: > On Wed, Apr 21, 2021 at 11:26:08AM +0200, Uwe Kleine-König wrote: > > With these three patches PWM_DEBUG is now happy. (At least I couldn't > > trigger a warning any more. I think there are still a few problems with > > integer overflows.) > > BTW, setting the period to 138350580899 (with a clock rate of 133333333 > Hz) results in setting period=0 because > > state->period * clkrate = > 138350580899 * 133333333 = > 40254751 (discarded from 18446744073749806367). As a first remedy the following could be done: diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c index 38d86340201c..02d69fa5f7d2 100644 --- a/drivers/pwm/pwm-atmel.c +++ b/drivers/pwm/pwm-atmel.c @@ -199,6 +199,11 @@ static int atmel_pwm_calculate_cprd_and_pres(struct pwm_chip *chip, unsigned long long cycles = state->period; int shift; + if (fls(cycles) + fls(clkrate) > 64) { + dev_err(chip->dev, "period to big to calculate HW parameters\n"); + return -EINVAL; + } + /* Calculate the period cycles and prescale value */ cycles *= clkrate; do_div(cycles, NSEC_PER_SEC); Is this sensible? (Actually I'd prefer to just continue with period = (ULL(1) << (64 - fls(clkrate))) - 1 according to the motto to yield the highest possible period, but this function has another error path that returns -EINVAL so this would be inconsistent.) Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ | [-- Attachment #2: signature.asc --] [-- Type: application/pgp-signature, Size: 488 bytes --]
WARNING: multiple messages have this Message-ID (diff)
From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de> To: Claudiu Beznea <claudiu.beznea@microchip.com>, Thierry Reding <thierry.reding@gmail.com>, Lee Jones <lee.jones@linaro.org> Cc: linux-pwm@vger.kernel.org, Alexandre Belloni <alexandre.belloni@bootlin.com>, Ludovic Desroches <ludovic.desroches@microchip.com>, kernel@pengutronix.de, linux-arm-kernel@lists.infradead.org Subject: Re: overflow and wrong timeout errors in pwm-atmel Date: Wed, 21 Apr 2021 15:48:25 +0200 [thread overview] Message-ID: <20210421134825.powx5tvqvce32fho@pengutronix.de> (raw) In-Reply-To: <20210421110336.bd5s6e2kjxqilddi@pengutronix.de> [-- Attachment #1.1: Type: text/plain, Size: 1628 bytes --] On Wed, Apr 21, 2021 at 01:03:36PM +0200, Uwe Kleine-König wrote: > On Wed, Apr 21, 2021 at 11:26:08AM +0200, Uwe Kleine-König wrote: > > With these three patches PWM_DEBUG is now happy. (At least I couldn't > > trigger a warning any more. I think there are still a few problems with > > integer overflows.) > > BTW, setting the period to 138350580899 (with a clock rate of 133333333 > Hz) results in setting period=0 because > > state->period * clkrate = > 138350580899 * 133333333 = > 40254751 (discarded from 18446744073749806367). As a first remedy the following could be done: diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c index 38d86340201c..02d69fa5f7d2 100644 --- a/drivers/pwm/pwm-atmel.c +++ b/drivers/pwm/pwm-atmel.c @@ -199,6 +199,11 @@ static int atmel_pwm_calculate_cprd_and_pres(struct pwm_chip *chip, unsigned long long cycles = state->period; int shift; + if (fls(cycles) + fls(clkrate) > 64) { + dev_err(chip->dev, "period to big to calculate HW parameters\n"); + return -EINVAL; + } + /* Calculate the period cycles and prescale value */ cycles *= clkrate; do_div(cycles, NSEC_PER_SEC); Is this sensible? (Actually I'd prefer to just continue with period = (ULL(1) << (64 - fls(clkrate))) - 1 according to the motto to yield the highest possible period, but this function has another error path that returns -EINVAL so this would be inconsistent.) Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ | [-- Attachment #1.2: signature.asc --] [-- Type: application/pgp-signature, Size: 488 bytes --] [-- Attachment #2: Type: text/plain, Size: 176 bytes --] _______________________________________________ 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:[~2021-04-21 13:48 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-20 9:51 [PATCH 1/2] pwm: atmel: Fix duty cycle calculation in .get_state() Uwe Kleine-König 2021-04-20 9:51 ` Uwe Kleine-König 2021-04-20 9:51 ` [PATCH 2/2] pwm: atmel: Improve duty cycle calculation in .apply() Uwe Kleine-König 2021-04-20 9:51 ` Uwe Kleine-König 2021-04-23 17:07 ` Thierry Reding 2021-04-23 17:07 ` Thierry Reding 2021-04-21 9:26 ` [PATCH] pwm: atmel: rework tracking updates pending in hardware Uwe Kleine-König 2021-04-21 9:26 ` Uwe Kleine-König 2021-04-21 11:03 ` overflow and wrong timeout errors in pwm-atmel Uwe Kleine-König 2021-04-21 13:48 ` Uwe Kleine-König [this message] 2021-04-21 13:48 ` Uwe Kleine-König 2021-04-21 14:18 ` Alexandre Belloni 2021-04-21 14:18 ` Alexandre Belloni 2021-04-21 15:26 ` Uwe Kleine-König 2021-04-21 15:26 ` Uwe Kleine-König 2021-07-05 7:55 ` [PATCH] pwm: atmel: rework tracking updates pending in hardware Uwe Kleine-König 2021-07-05 7:55 ` Uwe Kleine-König 2021-04-23 17:07 ` [PATCH 1/2] pwm: atmel: Fix duty cycle calculation in .get_state() Thierry Reding 2021-04-23 17:07 ` Thierry Reding
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