linux-kernel - Re: [PATCH] drm/amd/powerplay: use ARRAY_SIZE() for size of array

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Date:	Thu, 12 May 2016 10:49:36 +0100
From:	Eric Engestrom <eric.engestrom@...tec.com>
To:	Muhammad Falak R Wani <falakreyaz@...il.com>
CC:	Christian Knig <christian.koenig@....com>,
	Nils Wallménius <nils.wallmenius@...il.com>,
	Jammy Zhou <Jammy.Zhou@....com>,
	<linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
	Alex Deucher <alexander.deucher@....com>,
	Rex Zhu <Rex.Zhu@....com>,
	Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH] drm/amd/powerplay: use ARRAY_SIZE() for size of array

On Wed, May 11, 2016 at 11:18:43PM +0530, Muhammad Falak R Wani wrote:
> Use ARRAY_SIZE() for the size calculation of the array. Also move the
> condition evaulation function out of the for loop.
> Although, any respectable c-compiler would optimize this and evaluate
> the function only once outside the loop, but the optimzation engine
> of gcc is bit brain-dead, and at times needs some hand holding.

`sizeof` is actually a compile-time thing, so at worst, if no
optimisation is made, the runtime result is a division of two
literals, eg. `for (i = 0; i < 64/8; i++)` (which I doubt any
compiler would leave as is anyway)

So, +1 on using ARRAY_SIZE, -1 on creating a new variable (which
is not even `const` btw)

> 
> Signed-off-by: Muhammad Falak R Wani <falakreyaz@...il.com>
> ---
>  drivers/gpu/drm/amd/powerplay/smumgr/cz_smumgr.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/powerplay/smumgr/cz_smumgr.c b/drivers/gpu/drm/amd/powerplay/smumgr/cz_smumgr.c
> index da18f44..718a551 100644
> --- a/drivers/gpu/drm/amd/powerplay/smumgr/cz_smumgr.c
> +++ b/drivers/gpu/drm/amd/powerplay/smumgr/cz_smumgr.c
> @@ -636,10 +636,11 @@ static int cz_smu_populate_firmware_entries(struct pp_smumgr *smumgr)
>  	int ret;
>  	enum cgs_ucode_id ucode_id;
>  	struct cgs_firmware_info info = {0};
> +	int n = ARRAY_SIZE(firmware_list);
>  
>  	cz_smu->driver_buffer_length = 0;
>  
> -	for (i = 0; i < sizeof(firmware_list)/sizeof(*firmware_list); i++) {
> +	for (i = 0; i < n; i++) {
>  
>  		firmware_type = cz_translate_firmware_enum_to_arg(smumgr,
>  					firmware_list[i]);
> -- 
> 1.9.1
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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