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

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Message-ID: <5056c156-9f6c-8e0d-54e8-5317fdd46c12@pengutronix.de>
Date:   Fri, 6 Nov 2020 09:44:35 +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

On 11/6/20 8:41 AM, Lee Jones wrote:
> On Thu, 05 Nov 2020, Ahmad Fatoum wrote:
> 
>> 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?
> 
> From what I saw, it only void casts the ones which aren't assigned.

How do you mean? I wonder if

 #define for_each_oldnew_crtc_in_state(__state, crtc, old_crtc_state, new_crtc_state, __i) \
        for ((__i) = 0;                                                 \
             (__i) < (__state)->dev->mode_config.num_crtc;              \
             (__i)++)                                                   \
                for_each_if ((__state)->crtcs[__i].ptr &&               \
                             ((crtc) = (__state)->crtcs[__i].ptr,       \
                              (void)(crtc) /* Only to avoid unused-but-set-variable warning */, \
                             (old_crtc_state) = (__state)->crtcs[__i].old_state, \
                             (void)(old_crtc_state) /* Only to avoid unused-but-set-variable warning */, \
-                            (new_crtc_state) = (__state)->crtcs[__i].new_state, 1))
+                            (new_crtc_state) = (__state)->crtcs[__i].new_state, \
+                            (void)(new_crtc_state), 1))

wouldn't be better.

> 
>>> 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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