linux-kernel - Re: [PATCH 00/12] scsi/NCR5380: fix debugging macros and #include structure

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Date:	Wed, 19 Mar 2014 10:14:22 +1100 (EST)
From:	Finn Thain <fthain@...egraphics.com.au>
To:	Joe Perches <joe@...ches.com>
cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	scsi <linux-scsi@...r.kernel.org>, Sam Creasey <sammy@...my.net>,
	Russell King <linux@....linux.org.uk>,
	Michael Schmitz <schmitz@...ian.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux/m68k <linux-m68k@...r.kernel.org>
Subject: Re: [PATCH 00/12] scsi/NCR5380: fix debugging macros and #include
 structure


On Tue, 18 Mar 2014, Joe Perches wrote:

> On Tue, 2014-03-18 at 13:55 +0100, Geert Uytterhoeven wrote:

> > 
> > #define dprintk(flg, fmt, ...) no_printk(fmt, ##__VA_ARGS__)
> 
> Fine, but with a correction.
> 
> no_printk keeps all side effects like performing any function calls made 
> by the statement or accessing any volatiles.
> 
> Using
> 
> do { if (0) no_printk(fmt, ##__VA_ARGS__); } while (0)
> 
> does not have any side-effects.

I take your point about having the compiler check arguments when
NDEBUG & flg == 0.

As for side-effects, chip register accesses would be affected if dprintk() 
expanded to no_printk() when NDEBUG & flg == 0.

E.g. NCR5380.c line 1213:
dprintk(NDEBUG_INTR, "scsi : unknown interrupt, BASR 0x%X, MR 0x%X, SR 0x%x\n",
                     basr, NCR5380_read(MODE_REG), NCR5380_read(STATUS_REG));

I don't want to re-introduce side-effects into a dozen different NCR5380 
drivers on three different architectures when I can test only one of those 
drivers. It's difficult to get good code coverage even for one driver.

-- 
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