linux-kernel - Re: [PATCH] drm/tegra: vic: fix unused-function warnings

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Message-ID: <Yk2TwyteFgeqkZE1@orome>
Date:   Wed, 6 Apr 2022 15:21:07 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Dmitry Osipenko <digetx@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Robin Murphy <robin.murphy@....com>,
        dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/tegra: vic: fix unused-function warnings

On Wed, Mar 16, 2022 at 07:36:47PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The use of the old-style SET_RUNTIME_PM_OPS() and
> SET_SYSTEM_SLEEP_PM_OPS() macros requires function definitions
> to be hidden to avoid
> 
> drivers/gpu/drm/tegra/vic.c:326:12: error: 'vic_runtime_suspend' defined but not used [-Werror=unused-function]
>   326 | static int vic_runtime_suspend(struct device *dev)
>       |            ^~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/tegra/vic.c:292:12: error: 'vic_runtime_resume' defined but not used [-Werror=unused-function]
>   292 | static int vic_runtime_resume(struct device *dev)
>       |            ^~~~~~~~~~~~~~~~~~
> 
> Use the new-style SYSTEM_SLEEP_PM_OPS() and RUNTIME_PM_OPS() instead.
> 
> Fixes: 1e15f5b911d6 ("drm/tegra: vic: Stop channel on suspend")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/gpu/drm/tegra/vic.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> I see this warning on 5.17-rc8, but did not test it on linux-next,
> which may already have a fix.
> 
> diff --git a/drivers/gpu/drm/tegra/vic.c b/drivers/gpu/drm/tegra/vic.c
> index 1e342fa3d27b..f56f5921a8c2 100644
> --- a/drivers/gpu/drm/tegra/vic.c
> +++ b/drivers/gpu/drm/tegra/vic.c
> @@ -513,9 +513,8 @@ static int vic_remove(struct platform_device *pdev)
>  }
>  
>  static const struct dev_pm_ops vic_pm_ops = {
> -	SET_RUNTIME_PM_OPS(vic_runtime_suspend, vic_runtime_resume, NULL)
> -	SET_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
> -				pm_runtime_force_resume)
> +	RUNTIME_PM_OPS(vic_runtime_suspend, vic_runtime_resume, NULL)
> +	SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend, pm_runtime_force_resume)
>  };
>  
>  struct platform_driver tegra_vic_driver = {

Hi Arnd,

is this a replacement for __maybe_unused annotations that we would
typically use to address these? Is the ternary operator in PTR_IF enough
to eliminate the warning? Does that work the same way for structure
definitions as it does for conditionals where we use IS_ENABLED() to use
the compiler's DCE for improved coverage?

It looks like it, but just making sure because there's another patch
that fixes this warning by adding __maybe_unused.

Thierry

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