From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Billy Tsai <billy_tsai@aspeedtech.com>
Cc: "lee.jones@linaro.org" <lee.jones@linaro.org>,
"robh+dt@kernel.org" <robh+dt@kernel.org>,
"joel@jms.id.au" <joel@jms.id.au>,
"andrew@aj.id.au" <andrew@aj.id.au>,
"thierry.reding@gmail.com" <thierry.reding@gmail.com>,
"p.zabel@pengutronix.de" <p.zabel@pengutronix.de>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-aspeed@lists.ozlabs.org" <linux-aspeed@lists.ozlabs.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>,
BMC-SW <BMC-SW@aspeedtech.com>
Subject: Re: [v8 2/2] pwm: Add Aspeed ast2600 PWM support
Date: Fri, 9 Jul 2021 07:53:25 +0200 [thread overview]
Message-ID: <20210709055325.4y4ufjvoiwo2pcvi@pengutronix.de> (raw)
In-Reply-To: <FC122EAB-46A9-4B6F-B75C-271B4E17F057@aspeedtech.com>
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Hello Billy,
On Fri, Jul 09, 2021 at 05:40:45AM +0000, Billy Tsai wrote:
> On 2021/7/2, 10:32 PM, "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de> wrote:
> > The multiplication can be up to:
>
> > 100000000 * (1 << 31) * (31 + 1) * (255 + 1)
>
> > right? This needs 71 bits and so might overflow a u64.
>
> No, the multiplication can be up to:
>
> Max(div_h) = 15
> Max(div_l) = 255
> Max(clk_period) = 255
> 1000000000 * (1 << 15) * (255 + 1) * (255 + 1) < 2^64 - 1
> it doesn't overflow a u64.
Ah, you're right. Please note this in a comment (not that you were
right, but that it doesn't overflow :-)
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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WARNING: multiple messages have this Message-ID (diff)
From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Billy Tsai <billy_tsai@aspeedtech.com>
Cc: "lee.jones@linaro.org" <lee.jones@linaro.org>,
"robh+dt@kernel.org" <robh+dt@kernel.org>,
"joel@jms.id.au" <joel@jms.id.au>,
"andrew@aj.id.au" <andrew@aj.id.au>,
"thierry.reding@gmail.com" <thierry.reding@gmail.com>,
"p.zabel@pengutronix.de" <p.zabel@pengutronix.de>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-aspeed@lists.ozlabs.org" <linux-aspeed@lists.ozlabs.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>,
BMC-SW <BMC-SW@aspeedtech.com>
Subject: Re: [v8 2/2] pwm: Add Aspeed ast2600 PWM support
Date: Fri, 9 Jul 2021 07:53:25 +0200 [thread overview]
Message-ID: <20210709055325.4y4ufjvoiwo2pcvi@pengutronix.de> (raw)
In-Reply-To: <FC122EAB-46A9-4B6F-B75C-271B4E17F057@aspeedtech.com>
[-- Attachment #1.1: Type: text/plain, Size: 824 bytes --]
Hello Billy,
On Fri, Jul 09, 2021 at 05:40:45AM +0000, Billy Tsai wrote:
> On 2021/7/2, 10:32 PM, "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de> wrote:
> > The multiplication can be up to:
>
> > 100000000 * (1 << 31) * (31 + 1) * (255 + 1)
>
> > right? This needs 71 bits and so might overflow a u64.
>
> No, the multiplication can be up to:
>
> Max(div_h) = 15
> Max(div_l) = 255
> Max(clk_period) = 255
> 1000000000 * (1 << 15) * (255 + 1) * (255 + 1) < 2^64 - 1
> it doesn't overflow a u64.
Ah, you're right. Please note this in a comment (not that you were
right, but that it doesn't overflow :-)
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:[~2021-07-09 5:53 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-08 6:46 [v8 0/2] Support pwm driver for aspeed ast26xx Billy Tsai
2021-06-08 6:46 ` Billy Tsai
2021-06-08 6:46 ` [v8 1/2] dt-bindings: Add bindings for aspeed pwm-tach Billy Tsai
2021-06-08 6:46 ` Billy Tsai
2021-06-08 6:46 ` [v8 2/2] pwm: Add Aspeed ast2600 PWM support Billy Tsai
2021-06-08 6:46 ` Billy Tsai
2021-07-02 14:31 ` Uwe Kleine-König
2021-07-02 14:31 ` Uwe Kleine-König
2021-07-09 5:40 ` Billy Tsai
2021-07-09 5:40 ` Billy Tsai
2021-07-09 5:53 ` Uwe Kleine-König [this message]
2021-07-09 5:53 ` Uwe Kleine-König
2021-07-09 5:59 ` Billy Tsai
2021-07-09 5:59 ` Billy Tsai
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