linux-kernel - Re: [PATCH 1/2] comedi: dmm32at: Fix coding style

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Date:	Wed, 18 Nov 2015 17:02:50 +0000
From:	Ian Abbott <abbotti@....co.uk>
To:	Hartley Sweeten <HartleyS@...ionengravers.com>,
	Ranjith Thangavel <ranjithece24@...il.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc:	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] comedi: dmm32at: Fix coding style - use BIT macro

On 18/11/15 16:45, Hartley Sweeten wrote:
> On Wednesday, November 18, 2015 9:42 AM, Ian Abbott wrote:
>> On 16/11/15 17:18, Ranjith Thangavel wrote:
>   [snip]
>>> -#define DMM32AT_AI_CFG_SCINT_20US	(0 << 4)
>>> -#define DMM32AT_AI_CFG_SCINT_15US	(1 << 4)
>>> -#define DMM32AT_AI_CFG_SCINT_10US	(2 << 4)
>>> -#define DMM32AT_AI_CFG_SCINT_5US	(3 << 4)
>>> -#define DMM32AT_AI_CFG_RANGE		(1 << 3)  /* 0=5V  1=10V */
>>> -#define DMM32AT_AI_CFG_ADBU		(1 << 2)  /* 0=bipolar  1=unipolar */
>>> +#define DMM32AT_AI_CFG_SCINT_20US	0
>>> +#define DMM32AT_AI_CFG_SCINT_15US	BIT(4)
>>> +#define DMM32AT_AI_CFG_SCINT_10US	(BIT(5) & ~BIT(4))
>>
>> The `(BIT(5) & ~BIT(4))` is a bit ugly.  You can just use `BIT(5)` to
>> fit in with the style of your other changes.
>>
>>   (Personally though, I don't think BIT() is appropriate for shifted,
>> multi-bit values.)
>
> It would be more appropriate as a macro:
>
> #define DMM32AT_AI_CFG_SCINT(x)		(((x) & 0x3) << 4)
> #define DMM32AT_AI_CFG_SCINT_20US	DMM32AT_AI_CFG_SCINT (0)
> #define DMM32AT_AI_CFG_SCINT_15US	DMM32AT_AI_CFG_SCINT (1)
> #define DMM32AT_AI_CFG_SCINT_10US	DMM32AT_AI_CFG_SCINT (2)
> #define DMM32AT_AI_CFG_SCINT_5US	DMM32AT_AI_CFG_SCINT (3)

Yes, but without the spaces in the macro calls!

It's slightly surprising no one has pushed a generic macro for this sort 
of thing, maybe something like:

#define MBIT(v, s)	((v) * BIT(s))

although the name sucks - maybe the problem is thinking up a decent name!

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@....co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-
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