From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Conor Dooley <conor.dooley@microchip.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
Daire McNamara <daire.mcnamara@microchip.com>,
linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org,
linux-riscv@lists.infradead.org
Subject: Re: [PATCH v17 1/2] pwm: add microchip soft ip corePWM driver
Date: Wed, 17 May 2023 12:20:30 +0200 [thread overview]
Message-ID: <20230517102030.b4nyo2dmpfl7v7fk@pengutronix.de> (raw)
In-Reply-To: <20230421-sleek-bottom-88b867f56609@wendy>
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Hello Conor,
I found one remaining issue:
On Fri, Apr 21, 2023 at 10:27:09AM +0100, Conor Dooley wrote:
> +static u64 mchp_core_pwm_calc_duty(const struct pwm_state *state, u64 clk_rate,
> + u8 prescale, u8 period_steps)
> +{
> + u64 duty_steps, tmp;
> +
> + /*
> + * Calculate the duty cycle in multiples of the prescaled period:
> + * duty_steps = duty_in_ns / step_in_ns
> + * step_in_ns = (prescale * NSEC_PER_SEC) / clk_rate
> + * The code below is rearranged slightly to only divide once.
> + */
> + tmp = (prescale + 1) * NSEC_PER_SEC;
If prescale > 4 this overflows on 32bit archs, doesn't it?
(I think prescale + 1 is promoted to unsigned int, then the
multiplication is done and only then the range is extended to u64.
> + duty_steps = mul_u64_u64_div_u64(state->duty_cycle, clk_rate, tmp);
> +
> + return duty_steps;
> +}
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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next prev parent reply other threads:[~2023-05-17 10:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-21 9:27 [PATCH v17 0/2] Microchip Soft IP corePWM driver Conor Dooley
2023-04-21 9:27 ` [PATCH v17 1/2] pwm: add microchip soft ip " Conor Dooley
2023-05-17 10:20 ` Uwe Kleine-König [this message]
2023-05-17 10:57 ` Conor Dooley
2023-04-21 9:27 ` [PATCH v17 2/2] MAINTAINERS: add pwm to PolarFire SoC entry Conor Dooley
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