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From:   "Chrisanthus, Anitha" <anitha.chrisanthus@intel.com>
To:     Arnd Bergmann <arnd@kernel.org>,
        "Dea, Edmund J" <edmund.j.dea@intel.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        "Sam Ravnborg" <sam@ravnborg.org>
CC:     Arnd Bergmann <arnd@arndb.de>, lkp <lkp@intel.com>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] drm/kmb: fix array bounds warning
Thread-Topic: [PATCH] drm/kmb: fix array bounds warning
Thread-Index: AQHWxouYX6RKw2p6RUm12CsNuNmoW6nhP/Ug
Date:   Mon, 30 Nov 2020 22:19:13 +0000
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References: <20201129200927.1854104-1-arnd@kernel.org>
In-Reply-To: <20201129200927.1854104-1-arnd@kernel.org>
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Hi Arnd,
Thanks for your patch.

> -----Original Message-----
> From: Arnd Bergmann <arnd@kernel.org>
> Sent: Sunday, November 29, 2020 12:09 PM
> To: Chrisanthus, Anitha <anitha.chrisanthus@intel.com>; Dea, Edmund J
> <edmund.j.dea@intel.com>; David Airlie <airlied@linux.ie>; Daniel Vetter
> <daniel@ffwll.ch>; Sam Ravnborg <sam@ravnborg.org>
> Cc: Arnd Bergmann <arnd@arndb.de>; lkp <lkp@intel.com>; dri-
> devel@lists.freedesktop.org; linux-kernel@vger.kernel.org
> Subject: [PATCH] drm/kmb: fix array bounds warning
>=20
> From: Arnd Bergmann <arnd@arndb.de>
>=20
> gcc warns about an out-of-bounds access when the using nonzero
> values for 'plane_id' on kmb->plane_status:
>=20
> drivers/gpu/drm/kmb/kmb_plane.c: In function 'kmb_plane_atomic_disable':
> drivers/gpu/drm/kmb/kmb_plane.c:128:20: warning: array subscript 3 is
> above array bounds of 'struct layer_status[1]' [-Warray-bounds]
>   128 |   kmb->plane_status[plane_id].ctrl =3D LCD_CTRL_GL2_ENABLE;
>       |   ~~~~~~~~~~~~~~~~~^~~~~~~~~~
> drivers/gpu/drm/kmb/kmb_plane.c:125:20: warning: array subscript 2 is
> above array bounds of 'struct layer_status[1]' [-Warray-bounds]
>   125 |   kmb->plane_status[plane_id].ctrl =3D LCD_CTRL_GL1_ENABLE;
>       |   ~~~~~~~~~~~~~~~~~^~~~~~~~~~
> drivers/gpu/drm/kmb/kmb_plane.c:122:20: warning: array subscript 1 is
> above array bounds of 'struct layer_status[1]' [-Warray-bounds]
>   122 |   kmb->plane_status[plane_id].ctrl =3D LCD_CTRL_VL2_ENABLE;
>=20
> Having the array truncated to one entry seems intentional, so add
> a range check before indexing it to make it clearer what is going
> on and shut up the warning.
>=20
> I received the warning from the kernel test robot after a private
> patch that turns on Warray-bounds unconditionally.
>=20
> Fixes: 7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display")
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/gpu/drm/kmb/kmb_plane.c | 3 +++
>  1 file changed, 3 insertions(+)
>=20
> diff --git a/drivers/gpu/drm/kmb/kmb_plane.c
> b/drivers/gpu/drm/kmb/kmb_plane.c
> index 8448d1edb553..be8eea3830c1 100644
> --- a/drivers/gpu/drm/kmb/kmb_plane.c
> +++ b/drivers/gpu/drm/kmb/kmb_plane.c
> @@ -114,6 +114,9 @@ static void kmb_plane_atomic_disable(struct
> drm_plane *plane,
>=20
>  	kmb =3D to_kmb(plane->dev);
>=20
> +	if (WARN_ON(plane_id >=3D KMB_MAX_PLANES))
> +		return;
> +
Looks good.

Reviewed-by: Anitha Chrisanthus <anitha.chrisanthus@intel.com>
>  	switch (plane_id) {
>  	case LAYER_0:
>  		kmb->plane_status[plane_id].ctrl =3D LCD_CTRL_VL1_ENABLE;
> --
> 2.27.0