linux-kernel - Re: [PATCH 03/19] gpu: drm: imx: ipuv3-plane: Mark 'crtc_state' as __always

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Date:   Thu, 5 Nov 2020 20:17:26 +0100
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Fabio Estevam <festevam@...il.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        NXP Linux Team <linux-imx@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        Shawn Guo <shawnguo@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>
Subject: Re: [PATCH 03/19] gpu: drm: imx: ipuv3-plane: Mark 'crtc_state' as
 __always_unused

Hello Lee,

On 11/5/20 3:45 PM, Lee Jones wrote:
> In the macro for_each_oldnew_crtc_in_state() 'crtc_state' is provided
> as a container for state->crtcs[i].new_state, but is not utilised in
> this use-case.  We cannot simply delete the variable, so here we tell
> the compiler that we're intentionally discarding the read value.

for_each_oldnew_crtc_in_state already (void) casts the drm_crtc and the old
drm_crtc_state to silence unused-but-set-variable warning. Should we maybe
(void) cast the new crtc_state as well?

Cheers
Ahmad

> 
> Fixes the following W=1 kernel build warning(s):
> 
>  drivers/gpu/drm/imx/ipuv3-plane.c: In function ‘ipu_planes_assign_pre’:
>  drivers/gpu/drm/imx/ipuv3-plane.c:746:42: warning: variable ‘crtc_state’ set but not used [-Wunused-but-set-variable]
> 
> Cc: Philipp Zabel <p.zabel@...gutronix.de>
> Cc: David Airlie <airlied@...ux.ie>
> Cc: Daniel Vetter <daniel@...ll.ch>
> Cc: Shawn Guo <shawnguo@...nel.org>
> Cc: Sascha Hauer <s.hauer@...gutronix.de>
> Cc: Pengutronix Kernel Team <kernel@...gutronix.de>
> Cc: Fabio Estevam <festevam@...il.com>
> Cc: NXP Linux Team <linux-imx@....com>
> Cc: dri-devel@...ts.freedesktop.org
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---
>  drivers/gpu/drm/imx/ipuv3-plane.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/imx/ipuv3-plane.c b/drivers/gpu/drm/imx/ipuv3-plane.c
> index 8a4235d9d9f1e..acc0a3ce4992f 100644
> --- a/drivers/gpu/drm/imx/ipuv3-plane.c
> +++ b/drivers/gpu/drm/imx/ipuv3-plane.c
> @@ -743,7 +743,7 @@ bool ipu_plane_atomic_update_pending(struct drm_plane *plane)
>  int ipu_planes_assign_pre(struct drm_device *dev,
>  			  struct drm_atomic_state *state)
>  {
> -	struct drm_crtc_state *old_crtc_state, *crtc_state;
> +	struct drm_crtc_state *old_crtc_state, __always_unused *crtc_state;
>  	struct drm_plane_state *plane_state;
>  	struct ipu_plane_state *ipu_state;
>  	struct ipu_plane *ipu_plane;
> 

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