Hello Billy, On Mon, May 17, 2021 at 02:53:44AM +0000, Billy Tsai wrote: > On 2021/5/15, 11:57 PM,Uwe Kleine-Königwrote: > > > > + div_h = DIV_ROUND_DOWN_ULL(div_h, > > > + (FIELD_MAX(PWM_ASPEED_CTRL_CLK_DIV_L) + 1)); > > > + div_h = DIV_ROUND_DOWN_ULL(div_h, NSEC_PER_SEC); > > > As a division is an expensive operation you can better first multiply > > NSEC_PER_SEC and FIELD_MAX(PWM_ASPEED_CTRL_CLK_DIV_L) + 1 and divide by > > the result. > > When I multiply NSEC_PER_SEC and FIELD_MAX(PWM_ASPEED_CTRL_CLK_DIV_L) + 1 the result will overflow > for 32-bits and the divisor type of do_div is 32-bits so I need to do div twice to avoid the issue. > Can you give me some suggests? Hmm, you're right. There doesn't seem to be a div64_64, I thought there was one. Anyhow, while looking at the various divide functions I saw that dividing by a constant shouldn't be that expensive, so I think the sane way is to keep the two divisions and add a comment describing the problem. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |
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