linux-kernel - Re: [PATCH v3 1/7] clk: divider: add flag to limit possible dividers to even numbers

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Date:	Tue, 11 Jun 2013 15:37:27 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Heiko Stübner <heiko@...ech.de>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Chris Ball <cjb@...top.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Devicetree Discuss <devicetree-discuss@...ts.ozlabs.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Subject: Re: [PATCH v3 1/7] clk: divider: add flag to limit possible dividers
 to even numbers

On Tue, Jun 11, 2013 at 3:06 PM, Heiko Stübner <heiko@...ech.de> wrote:
> Am Dienstag, 11. Juni 2013, 13:51:56 schrieb Andy Shevchenko:
>> On Tue, Jun 11, 2013 at 2:29 PM, Heiko Stübner <heiko@...ech.de> wrote:

[]

>> > @@ -141,6 +149,8 @@ static bool _is_valid_div(struct clk_divider
>> > *divider, unsigned int div)
>> >
>> >                 return is_power_of_2(div);
>> >
>> >         if (divider->table)
>> >
>> >                 return _is_valid_table_div(divider->table, div);
>> >
>> > +       if (divider->flags & CLK_DIVIDER_EVEN && div != 1 && (div % 2) !=
>> > 0) +               return false;
>> >
>> >         return true;
>> >
>> >  }
>>
>> What if rewrite like
>>
>>  if (divider->flags & CLK_DIVIDER_EVEN == 0)
>>  return true;
>>
>> return div < 2 || div % 2 == 0;
>
> hmm, the current structure is of the form of testing for each feature and
> doing a applicable action if the flag is set. So it also is extensible for
> future flags and checking for the absence of an attribute while the rest of
> the conditionals check for the presence also might make the code harder to
> read.
>
> So for me the current variant somehow looks more intuitive.

This variant I think fits:

if (!(divider->flags & CLK_DIVIDER_EVEN))
  return div < 2 || div % 2 == 0;

You check for feature and do accordingly.

--
With Best Regards,
Andy Shevchenko
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