linux-kernel - Re: [PATCH v2 2/2] spi: add SPI controller driver for UniPhier SoC

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Date:   Thu, 26 Jul 2018 17:01:36 +0000
From:   Trent Piepho <tpiepho@...inj.com>
To:     "andy.shevchenko@...il.com" <andy.shevchenko@...il.com>,
        "hayashibara.keiji@...ionext.com" <hayashibara.keiji@...ionext.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "masami.hiramatsu@...aro.org" <masami.hiramatsu@...aro.org>,
        "hayashi.kunihiko@...ionext.com" <hayashi.kunihiko@...ionext.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "yamada.masahiro@...ionext.com" <yamada.masahiro@...ionext.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "jaswinder.singh@...aro.org" <jaswinder.singh@...aro.org>
Subject: Re: [PATCH v2 2/2] spi: add SPI controller driver for UniPhier SoC

On Thu, 2018-07-26 at 11:46 +0300, Andy Shevchenko wrote:
> > +
> > +       /*
> > +        * the supported rates are even numbers from 4 to 254. (4,6,8...254)
> > +        * round up as we look for equal or less speed
> > +        */
> > +       ckrat = DIV_ROUND_UP(clk_get_rate(priv->clk), speed);
> > +       ckrat = roundup(ckrat, 2);
> 
> ckrat += ckrat & 1;

Either way, the compiler produces the same code:

 add r0, r0, #1
 bic r0, r0, #1

I.e., ckrat = (ckrat + 1) & ~1, one "add" and one "and".

Might as well use the macro so it's clear. There is also round_up(x,y),
which I believe is intended to be used only with power of 2 values of
y.