linux-kernel - Re: [PATCH] drivers/bus: arm-cci: fix build warnings

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Message-ID: <0db1b8cd-b695-6cbf-9b27-f632b76bad11@arm.com>
Date:   Tue, 29 May 2018 16:34:01 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Arnd Bergmann <arnd@...db.de>, Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>
Cc:     Punit Agrawal <punit.agrawal@....com>,
        Rob Herring <robh@...nel.org>,
        Marc Zyngier <marc.zyngier@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/bus: arm-cci: fix build warnings

On 28/05/18 16:41, Arnd Bergmann wrote:
> When the arm-cci driver is enabled, but both CONFIG_ARM_CCI5xx_PMU and
> CONFIG_ARM_CCI400_PMU are not, we get a warning about how parts of
> the driver are never used:
> 
> drivers/perf/arm-cci.c:1454:29: error: 'cci_pmu_models' defined but not used [-Werror=unused-variable]
> drivers/perf/arm-cci.c:693:16: error: 'cci_pmu_event_show' defined but not used [-Werror=unused-function]
> drivers/perf/arm-cci.c:685:16: error: 'cci_pmu_format_show' defined but not used [-Werror=unused-function]
> 
> Marking all three functions as __maybe_unused avoids the warnings in
> randconfig builds. I'm doing this lacking any ideas for a better fix.

Yeah, it's a bit of a silly configuration to allow building a driver 
supporting no PMU types, but I couldn't find a way to enforce "at least 
one sub-option enabled" logic without introducing mutually-exclusive 
dependencies which kbuild thinks are recursive.

An alternative would be to remove the CCI400/CCI5x0 configurability 
altogether - I've not not looked in detail at how much difference that 
actually makes.

Otherwise, as an immediate quick-fix:

Reviewed-by: Robin Murphy <robin.murphy@....com>

Thanks,
Robin.

> Fixes: 3de6be7a3dd8 ("drivers/bus: Split Arm CCI driver")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>   drivers/perf/arm-cci.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/perf/arm-cci.c b/drivers/perf/arm-cci.c
> index e6fadc8e1178..0d09d8e669cd 100644
> --- a/drivers/perf/arm-cci.c
> +++ b/drivers/perf/arm-cci.c
> @@ -120,9 +120,9 @@ enum cci_models {
>   
>   static void pmu_write_counters(struct cci_pmu *cci_pmu,
>   				 unsigned long *mask);
> -static ssize_t cci_pmu_format_show(struct device *dev,
> +static ssize_t __maybe_unused cci_pmu_format_show(struct device *dev,
>   			struct device_attribute *attr, char *buf);
> -static ssize_t cci_pmu_event_show(struct device *dev,
> +static ssize_t __maybe_unused cci_pmu_event_show(struct device *dev,
>   			struct device_attribute *attr, char *buf);
>   
>   #define CCI_EXT_ATTR_ENTRY(_name, _func, _config) 				\
> @@ -1451,7 +1451,7 @@ static int cci_pmu_offline_cpu(unsigned int cpu)
>   	return 0;
>   }
>   
> -static struct cci_pmu_model cci_pmu_models[] = {
> +static __maybe_unused struct cci_pmu_model cci_pmu_models[] = {
>   #ifdef CONFIG_ARM_CCI400_PMU
>   	[CCI400_R0] = {
>   		.name = "CCI_400",
>