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

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Date:   Mon, 30 Jul 2018 14:30:25 +0900
From:   "Keiji Hayashibara" <hayashibara.keiji@...ionext.com>
To:     "'Trent Piepho'" <tpiepho@...inj.com>, <andy.shevchenko@...il.com>
Cc:     <linux-kernel@...r.kernel.org>, <robh+dt@...nel.org>,
        <devicetree@...r.kernel.org>, <masami.hiramatsu@...aro.org>,
        Hayashi, Kunihiko/林 邦彦 
        <hayashi.kunihiko@...ionext.com>, <broonie@...nel.org>,
        <mark.rutland@....com>, <linux-spi@...r.kernel.org>,
        Yamada, Masahiro/山田 真弘 
        <yamada.masahiro@...ionext.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <jaswinder.singh@...aro.org>
Subject: RE: [PATCH v2 2/2] spi: add SPI controller driver for UniPhier SoC

Hello Trent and Andy,

> From: Trent Piepho [mailto:tpiepho@...inj.com]
> Sent: Friday, July 27, 2018 2:02 AM
> To: andy.shevchenko@...il.com; Hayashibara, Keiji/林原 啓二 <hayashibara.keiji@...ionext.com>
> 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.

I confirmed round_up() macro.
This macro is optimized to power of 2 argument,
and it matches to this case and clear.

I will replace to round_up() macro.

Thank you.

-----------------
Best Regards,
Keiji Hayashibara