From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dirk Behme <dirk.behme@googlemail.com>
Date: Mon, 10 Nov 2008 20:43:16 +0100
Subject: [U-Boot] [PATCH-OMAP3] OMAP3: Remove BITx magic
In-Reply-To: <4917f005.095c5e0a.027e.ffffc9bfSMTPIN_ADDED@mx.google.com>
References: <49172e4a.0b38560a.42bc.ffffb794@mx.google.com>
	<4917f005.095c5e0a.027e.ffffc9bfSMTPIN_ADDED@mx.google.com>
Message-ID: <49188ED4.5010307@googlemail.com>
List-Id: <u-boot.lists.denx.de>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: u-boot@lists.denx.de

Dear Wolfgang,

Wolfgang Denk wrote:
> Dear dirk.behme at googlemail.com,
> 
> In message <49172e4a.0b38560a.42bc.ffffb794@mx.google.com> you wrote:
> 
>>Subject: [PATCH-OMAP3] OMAP3: Remove BITx magic
>>
>>From: Dirk Behme <dirk.behme@gmail.com>
>>
>>Remove bits.h and it's macros usage. Requested by Wolfgang Denk.
>>
>>Signed-off-by: Dirk Behme <dirk.behme@gmail.com>
> 
> ...
> 
>> /* device type */
>>-#define DEVICE_MASK		(BIT8 | BIT9 | BIT10)
>>+#define DEVICE_MASK		(0x7 << 8)
> 
> 
> That's a funny way to make code difficult to read. Why do you prefer
> "(0x7 << 8)" instead of "0x700" (which looks more obvious to me) ?
> 
> 
>>-#define DLL_NO_FILTER_MASK	(BIT8 | BIT9)
>>+#define DLL_NO_FILTER_MASK	((0x1 << 9) | (0x1 << 8))
> 
> Ditto here - why not simply 0x300 ?

For my taste the << style makes it easier to create macros from TRM 
and later to review code against TRM.

Maybe 0x700 and 0x300 are easy cases, but for e.g

0x34B03C00

I need a sheet of paper or calculator to get an idea which bits are 
exactly set in register. And then later re-calculate twice to be sure 
I'm correct ;)

Having a TRM, looking@a register description and then wanting to 
set Bits 29 & 28 & 26 & 23 & 21 & 20 & 13 & 12 & 11 & 10 using 
something like

(1 << 29) | (1 << 28) | (1 << 26) | (1 << 23) | (1 << 21) | (1 << 20) 
| (1 << 13) | (1 << 12) | (1 << 11) | (1 << 10)

makes it more obvious for me. Then using preprocessor/compiler to 
create 0x34B03C00 I'm on the safe side from my point of view.

>>-#define GPT_EN			((0 << 2) | BIT1 | BIT0)
>>+#define GPT_EN			((0x0 << 2) | (0x1 << 1) | (0x1 << 0))
> 
> 
> Why not 0x3 ?
> 
> Note: especially the "(0x0 << 2) | " part in the expression i really
> bogus.

Again, from TRM point of view, above style makes it clear that bit 2 
is intentionally set to zero.

Best regards

Dirk