linux-kernel - Re: [PATCH] drm/rockchip: vop2: fix uninitialized variable possible

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Date:   Thu, 16 Mar 2023 15:05:46 +0100
From:   Heiko Stuebner <heiko@...ech.de>
To:     hjc@...k-chips.com, airlied@...il.com, daniel@...ll.ch,
        nathan@...nel.org, ndesaulniers@...gle.com,
        michael.riesch@...fvision.net, s.hauer@...gutronix.de,
        Tom Rix <trix@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Tom Rix <trix@...hat.com>
Subject: Re: [PATCH] drm/rockchip: vop2: fix uninitialized variable possible_crtcs

Am Donnerstag, 16. März 2023, 14:23:02 CET schrieb Tom Rix:
> clang reportes this error
> drivers/gpu/drm/rockchip/rockchip_drm_vop2.c:2322:8: error:
>   variable 'possible_crtcs' is used uninitialized whenever 'if'
>   condition is false [-Werror,-Wsometimes-uninitialized]
>                         if (vp) {
>                             ^~
> drivers/gpu/drm/rockchip/rockchip_drm_vop2.c:2336:36: note:
>   uninitialized use occurs here
>                 ret = vop2_plane_init(vop2, win, possible_crtcs);
>                                                  ^~~~~~~~~~~~~~
> drivers/gpu/drm/rockchip/rockchip_drm_vop2.c:2322:4:
>   note: remove the 'if' if its condition is always true
>                         if (vp) {
>                         ^~~~~~~~
> 
> The else-statement changes the win->type to OVERLAY without setting the
> possible_crtcs variable.  Rework the block, initialize possible_crtcs to
> 0 to remove the else-statement.  Split the else-if-statement out to its
> own if-statement so the OVERLAY check will catch when the win-type has
> been changed.
> 
> Fixes: 368419a2d429 ("drm/rockchip: vop2: initialize possible_crtcs properly")
> Signed-off-by: Tom Rix <trix@...hat.com>
> ---
>  drivers/gpu/drm/rockchip/rockchip_drm_vop2.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
> index 03ca32cd2050..fce992c3506f 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
> @@ -2301,7 +2301,7 @@ static int vop2_create_crtcs(struct vop2 *vop2)
>  	nvp = 0;
>  	for (i = 0; i < vop2->registered_num_wins; i++) {
>  		struct vop2_win *win = &vop2->win[i];
> -		u32 possible_crtcs;
> +		u32 possible_crtcs = 0;
>  
>  		if (vop2->data->soc_id == 3566) {
>  			/*
> @@ -2327,12 +2327,11 @@ static int vop2_create_crtcs(struct vop2 *vop2)
>  				/* change the unused primary window to overlay window */
>  				win->type = DRM_PLANE_TYPE_OVERLAY;
>  			}
> -		} else if (win->type == DRM_PLANE_TYPE_OVERLAY) {
> -			possible_crtcs = (1 << nvps) - 1;
> -		} else {
> -			possible_crtcs = 0;
>  		}
>  
> +		if (win->type == DRM_PLANE_TYPE_OVERLAY)
> +			possible_crtcs = (1 << nvps) - 1;
> +

After a long hard stare at the code in question, I think doing it this
way looks like the correct one, as as you mention in the commit message
the first "if" will change the win->type to OVERLAY in one case, but this
then will never be added.

Michael, do you agree/disagree?


Thanks
Heiko

https://lore.kernel.org/r/20230315090158.2442771-1-michael.riesch@wolfvision.net

>  		ret = vop2_plane_init(vop2, win, possible_crtcs);
>  		if (ret) {
>  			drm_err(vop2->drm, "failed to init plane %s: %d\n",
>