linux-kernel - Re: [PATCH] drm/mgag200: make a const array static, makes object smaller

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Date:   Thu, 4 Feb 2021 19:27:58 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Colin King <colin.king@...onical.com>,
        Dave Airlie <airlied@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/mgag200: make a const array static, makes object
 smaller

Hi

Am 04.02.21 um 19:17 schrieb Colin King:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Don't populate the const array m_div_val on the stack but instead make
> it static. Makes the object code smaller by 29 bytes:
> 
> Before:
>     text	   data	  bss   dec    hex filename
>    34736	   4552	    0 39288   9978 drivers/gpu/drm/mgag200/mgag200_mode.o
> 
> After:
>     text	   data	  bss   dec    hex filename
>    34625	   4616	    0 39241   9949 drivers/gpu/drm/mgag200/mgag200_mode.o
> 
> (gcc version 10.2.0)
> 
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

Very nice. I'm actually surprised that the compiler doesn't figure this 
out automatically. When I once tested this (in userspace) it did so. 
Maybe the kernel is different?

For style reasons, I would have moved the static definition to the top 
of the function; before the variable declarations. In any case:

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

If I don't here from you, I'll merge the patch soonish.

Best regards
Thomas

> ---
>   drivers/gpu/drm/mgag200/mgag200_mode.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
> index 1dfc42170059..27f33af09798 100644
> --- a/drivers/gpu/drm/mgag200/mgag200_mode.c
> +++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
> @@ -712,7 +712,7 @@ static int mga_g200er_set_plls(struct mga_device *mdev, long clock)
>   	unsigned int p, m, n;
>   	unsigned int computed, vco;
>   	int tmp;
> -	const unsigned int m_div_val[] = { 1, 2, 4, 8 };
> +	static const unsigned int m_div_val[] = { 1, 2, 4, 8 };
>   
>   	m = n = p = 0;
>   	vcomax = 1488000;
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer



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