linux-kernel - Re: [PATCH 01/10] drm/imagination: avoid unused-const-variable warning

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Message-ID: <04e72a15-627a-4ca0-824b-a40add7cd4de@imgtec.com>
Date: Tue, 22 Apr 2025 16:08:19 +0000
From: Matt Coster <Matt.Coster@...tec.com>
To: Arnd Bergmann <arnd@...nel.org>
CC: Frank Binns <Frank.Binns@...tec.com>,
        Maarten Lankhorst
	<maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Krzysztof Kozlowski
	<krzysztof.kozlowski@...aro.org>,
        Andy Shevchenko
	<andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrzej
 Hajda <andrzej.hajda@...el.com>,
        Jani Nikula <jani.nikula@...el.com>,
        Alex
 Deucher <alexander.deucher@....com>,
        Alessio Belle
	<Alessio.Belle@...tec.com>,
        "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/10] drm/imagination: avoid unused-const-variable
 warning

On 09/04/2025 13:22, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> When CONFIG_DEBUG_FS is disabled, the stid_fmts[] array is not referenced
> anywhere, causing a W=1 warning with gcc:
> 
> In file included from drivers/gpu/drm/imagination/pvr_fw_trace.c:7:
> drivers/gpu/drm/imagination/pvr_rogue_fwif_sf.h:75:39: error: 'stid_fmts' defined but not used [-Werror=unused-const-variable=]
>    75 | static const struct rogue_km_stid_fmt stid_fmts[] = {
>       |                                       ^~~~~~~~~
> 
> Rather than adding more #ifdef blocks, address this by changing the
> existing #ifdef into equivalent IS_ENABLED() checks so gcc can see
> where the symbol is used but still eliminate it from the object file.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Hi Arnd,

After sleeping revisiting this after being on holiday, it seems like
enough of my concerns were due solely to my ignorance that I'd rather
just take this patch as-is than spend time reworking it. (Thanks to Jani
and Andi for filling gaps in my knowledge too!)

To that end,

Reviewed-by: Matt Coster <matt.coster@...tec.com>

And I'll take this through drm-misc-next tomorrow if there are no
objections.

Cheers,
Matt

> ---
>  drivers/gpu/drm/imagination/pvr_fw_trace.c | 8 ++++----
>  drivers/gpu/drm/imagination/pvr_fw_trace.h | 2 --
>  2 files changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/imagination/pvr_fw_trace.c b/drivers/gpu/drm/imagination/pvr_fw_trace.c
> index 5dbb636d7d4f..93269299d6a4 100644
> --- a/drivers/gpu/drm/imagination/pvr_fw_trace.c
> +++ b/drivers/gpu/drm/imagination/pvr_fw_trace.c
> @@ -122,8 +122,6 @@ void pvr_fw_trace_fini(struct pvr_device *pvr_dev)
>  	pvr_fw_object_unmap_and_destroy(fw_trace->tracebuf_ctrl_obj);
>  }
>  
> -#if defined(CONFIG_DEBUG_FS)
> -
>  /**
>   * update_logtype() - Send KCCB command to trigger FW to update logtype
>   * @pvr_dev: Target PowerVR device
> @@ -447,7 +445,7 @@ static const struct file_operations pvr_fw_trace_fops = {
>  void
>  pvr_fw_trace_mask_update(struct pvr_device *pvr_dev, u32 old_mask, u32 new_mask)
>  {
> -	if (old_mask != new_mask)
> +	if (IS_ENABLED(CONFIG_DEBUG_FS) && old_mask != new_mask)
>  		update_logtype(pvr_dev, new_mask);
>  }
>  
> @@ -457,6 +455,9 @@ pvr_fw_trace_debugfs_init(struct pvr_device *pvr_dev, struct dentry *dir)
>  	struct pvr_fw_trace *fw_trace = &pvr_dev->fw_dev.fw_trace;
>  	u32 thread_nr;
>  
> +	if (!IS_ENABLED(CONFIG_DEBUG_FS))
> +		return;
> +
>  	static_assert(ARRAY_SIZE(fw_trace->buffers) <= 10,
>  		      "The filename buffer is only large enough for a single-digit thread count");
>  
> @@ -469,4 +470,3 @@ pvr_fw_trace_debugfs_init(struct pvr_device *pvr_dev, struct dentry *dir)
>  				    &pvr_fw_trace_fops);
>  	}
>  }
> -#endif
> diff --git a/drivers/gpu/drm/imagination/pvr_fw_trace.h b/drivers/gpu/drm/imagination/pvr_fw_trace.h
> index 0074d2b18da0..1d0ef937427a 100644
> --- a/drivers/gpu/drm/imagination/pvr_fw_trace.h
> +++ b/drivers/gpu/drm/imagination/pvr_fw_trace.h
> @@ -65,7 +65,6 @@ struct pvr_fw_trace {
>  int pvr_fw_trace_init(struct pvr_device *pvr_dev);
>  void pvr_fw_trace_fini(struct pvr_device *pvr_dev);
>  
> -#if defined(CONFIG_DEBUG_FS)
>  /* Forward declaration from <linux/dcache.h>. */
>  struct dentry;
>  
> @@ -73,6 +72,5 @@ void pvr_fw_trace_mask_update(struct pvr_device *pvr_dev, u32 old_mask,
>  			      u32 new_mask);
>  
>  void pvr_fw_trace_debugfs_init(struct pvr_device *pvr_dev, struct dentry *dir);
> -#endif /* defined(CONFIG_DEBUG_FS) */
>  
>  #endif /* PVR_FW_TRACE_H */


-- 
Matt Coster
E: matt.coster@...tec.com


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