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Date:   Fri, 9 Jul 2021 07:53:25 +0200
From:   Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
To:     Billy Tsai <billy_tsai@aspeedtech.com>
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        "robh+dt@kernel.org" <robh+dt@kernel.org>,
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Subject: Re: [v8 2/2] pwm: Add Aspeed ast2600 PWM support
Message-ID: <20210709055325.4y4ufjvoiwo2pcvi@pengutronix.de>
References: <20210608064658.14262-1-billy_tsai@aspeedtech.com>
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 <20210702143147.6a7psfup4tlidq2x@pengutronix.de>
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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-K=F6nig" <u.kleine-koenig@pengutronix.=
de> wrote:
>     > The multiplication can be up to:
>=20
>     >	100000000 * (1 << 31) * (31 + 1) * (255 + 1)
>=20
>     > right? This needs 71 bits and so might overflow a u64.
>=20
> No, the multiplication can be up to:
>=20
> Max(div_h) =3D 15
> Max(div_l) =3D 255
> Max(clk_period) =3D 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

--=20
Pengutronix e.K.                           | Uwe Kleine-K=F6nig            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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