linux-kernel - Re: [PATCH] amba: tegra-ahb: mark PM functions as __maybe

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Message-ID: <20190426152033.GB19559@ulmo>
Date:   Fri, 26 Apr 2019 17:20:33 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Russell King <linux@...linux.org.uk>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] amba: tegra-ahb: mark PM functions as __maybe_unused

On Fri, Apr 26, 2019 at 04:56:03PM +0200, Arnd Bergmann wrote:
> clang warns about an unused variable when CONFIG_PM is disabled,
> since it is only referenced from an #ifdef:
> 
> drivers/amba/tegra-ahb.c:97:18: error: variable 'tegra_ahb_gizmo' is not needed and will not be emitted [-Werror,-Wunneeded-internal-declaration]
> 
> Rather than trying to get the #ifdef right, remove it and
> use __maybe_unused here, which is less error prone.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/amba/tegra-ahb.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)

Shouldn't tegra_ahb_gizmo have the same annotation, then? I do see that
it's "used" in tegra_ahb_probe() as part of an ARRAY_SIZE() expression,
but that technically doesn't mean that it would need to be emitted, but
it might be enough to shut up clang?

Or does the __maybe_unused not get propagated?

Looking at the code, I guess we could save a bit of memory if we didn't
allocate memory for the zero-length "ctx" array for !PM since that's no
longer needed. But then again, we've recently changed 32-bit Tegra to
forcefully enable PM, just like we did for 64-bit Tegra, so that's moot
anyway.

Do you want me to pick this up, or would you rather stash it into ARM
SoC directly? If the latter:

Acked-by: Thierry Reding <treding@...dia.com>

> diff --git a/drivers/amba/tegra-ahb.c b/drivers/amba/tegra-ahb.c
> index b0b688c481e8..3751d811be39 100644
> --- a/drivers/amba/tegra-ahb.c
> +++ b/drivers/amba/tegra-ahb.c
> @@ -170,8 +170,7 @@ int tegra_ahb_enable_smmu(struct device_node *dn)
>  EXPORT_SYMBOL(tegra_ahb_enable_smmu);
>  #endif
>  
> -#ifdef CONFIG_PM
> -static int tegra_ahb_suspend(struct device *dev)
> +static int __maybe_unused tegra_ahb_suspend(struct device *dev)
>  {
>  	int i;
>  	struct tegra_ahb *ahb = dev_get_drvdata(dev);
> @@ -181,7 +180,7 @@ static int tegra_ahb_suspend(struct device *dev)
>  	return 0;
>  }
>  
> -static int tegra_ahb_resume(struct device *dev)
> +static int __maybe_unused tegra_ahb_resume(struct device *dev)
>  {
>  	int i;
>  	struct tegra_ahb *ahb = dev_get_drvdata(dev);
> @@ -190,7 +189,6 @@ static int tegra_ahb_resume(struct device *dev)
>  		gizmo_writel(ahb, ahb->ctx[i], tegra_ahb_gizmo[i]);
>  	return 0;
>  }
> -#endif
>  
>  static UNIVERSAL_DEV_PM_OPS(tegra_ahb_pm,
>  			    tegra_ahb_suspend,
> -- 
> 2.20.0
> 

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