linux-kernel - Re: [PATCH] drm/edid: make a couple of read-only arrays static const

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Message-ID: <87o7tob0ze.fsf@intel.com>
Date:   Thu, 03 Nov 2022 15:51:01 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Colin Ian King <colin.i.king@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        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/edid: make a couple of read-only arrays static const

On Thu, 03 Nov 2022, Colin Ian King <colin.i.king@...il.com> wrote:
> Don't populate two read-only arrays on the stack but instead make
> them static const . Also makes the object code a little smaller.
>
> Signed-off-by: Colin Ian King <colin.i.king@...il.com>
> ---
>  drivers/gpu/drm/drm_edid.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 4671dc23abe0..50d488cc840e 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -3916,8 +3916,8 @@ static int drm_cvt_modes(struct drm_connector *connector,
>  	struct drm_display_mode *newmode;
>  	struct drm_device *dev = connector->dev;
>  	const struct cvt_timing *cvt;
> -	const int rates[] = { 60, 85, 75, 60, 50 };
> -	const u8 empty[3] = { 0, 0, 0 };
> +	static const int rates[] = { 60, 85, 75, 60, 50 };
> +	static const u8 empty[3] = { 0, 0, 0 };

The change is fine per se, but I think this whole array is silly. Could
be removed with:

-		if (!memcmp(cvt->code, empty, 3))
+		if (!memchr_inv(cvt->code, 0, sizeof(cvt->code)))


BR,
Jani.

PS. I also note that rates[0] is never used, but that's another story,
maybe a bug.


>  
>  	for (i = 0; i < 4; i++) {
>  		int width, height;

-- 
Jani Nikula, Intel Open Source Graphics Center