linux-kernel - Re: [PATCH 08/32] dmaengine: ste_dma40: Optimise local MAX() macro

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Message-ID: <20130425091544.GE4623@gmail.com>
Date:	Thu, 25 Apr 2013 10:15:44 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Linus WALLEIJ <linus.walleij@...ricsson.com>,
	Vinod Koul <vinod.koul@...el.com>, Dan Williams <djbw@...com>,
	Per Forlin <per.forlin@...ricsson.com>,
	Rabin Vincent <rabin@....in>
Subject: Re: [PATCH 08/32] dmaengine: ste_dma40: Optimise local MAX() macro

On Thu, 25 Apr 2013, Linus Walleij wrote:

> On Thu, Apr 18, 2013 at 12:11 PM, Lee Jones <lee.jones@...aro.org> wrote:
> 
> > The current implementation of the DMA40's local MAX() macro evaluates
> > its arguments more times than is necessary. This patch strips it
> > optimises it to only evaluate what's appropriate.
> >
> > Cc: Vinod Koul <vinod.koul@...el.com>
> > Cc: Dan Williams <djbw@...com>
> > Cc: Per Forlin <per.forlin@...ricsson.com>
> > Cc: Rabin Vincent <rabin@....in>
> > Reported-by: Harvey Harrison <harvey.harrison@...il.com>
> > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> (...)
> > -#define MAX(a, b) (((a) < (b)) ? (b) : (a))
> > +#define MAX(a, b) ((a > b) ? a : b)
> 
> Much has been said about this patch already, but notice what it is
> used for instead, one single thing at compile-time:
> 
> struct d40_base {
> (...)
>         u32
> reg_val_backup_v4[MAX(BACKUP_REGS_SZ_V4A, BACKUP_REGS_SZ_V4B)];
> (...)
> };
> 
> i.e. defining the size of that array at compile-time.
> 
> The actual size is figured out in d40_hw_detect_init().
> 
> So what about you just devm_kmalloc() that array instead and
> delete this macro. That is the real fix.

I'm happy to do it, but please see v2 of this patch first.

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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