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

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Date:	Thu, 25 Apr 2013 10:36:19 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Lee Jones <lee.jones@...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, 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.

Yours,
Linus Walleij
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