linux-kernel - Re: [PATCH 3/3] rtc: stm32: use 32-bit cast for BIT() macro

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Date:   Fri, 13 Jan 2017 16:56:54 +0100
From:   Amelie DELAUNAY <amelie.delaunay@...com>
To:     Arnd Bergmann <arnd@...db.de>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>
CC:     Mark Brown <broonie@...nel.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        "rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] rtc: stm32: use 32-bit cast for BIT() macro

Hi Arnd,

On 01/13/2017 04:32 PM, Arnd Bergmann wrote:
> Using the ~ operator on a BIT() constant results in a large 'unsigned long'
> constant that won't fit into an 'unsigned int' function argument on 64-bit
> architectures, resulting in a harmless build warning in x86 allmodconfig:
>
> drivers/rtc/rtc-stm32.c: In function 'stm32_rtc_probe':
> drivers/rtc/rtc-stm32.c:651:51: error: large integer implicitly truncated to unsigned type [-Werror=overflow]
>   regmap_update_bits(rtc->dbp, PWR_CR, PWR_CR_DBP, ~PWR_CR_DBP);
I thought I would fix this warning by replacing all ~PWR_CR_DBP by 0, 
because the mask PWR_CR_DBP prevents other bits to be cleared.
In this way, I avoid the ugly cast...
>
> This works around the warning by adding an explict cast to 'u32', but
> that is unfortunately a bit ugly and I feel there should be a better
> way to do this, possibly with some changes to either the bitops.h
> header or the regmap API.
>
> Cc: Mark Brown <broonie@...nel.org>
> Fixes: 4e64350f42e2 ("rtc: add STM32 RTC driver")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/rtc/rtc-stm32.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/rtc/rtc-stm32.c b/drivers/rtc/rtc-stm32.c
> index 8c599f52124c..05d3dc89e55f 100644
> --- a/drivers/rtc/rtc-stm32.c
> +++ b/drivers/rtc/rtc-stm32.c
> @@ -92,7 +92,7 @@
>  /* STM32_PWR_CR */
>  #define PWR_CR				0x00
>  /* STM32_PWR_CR bit field */
> -#define PWR_CR_DBP			BIT(8)
> +#define PWR_CR_DBP			(u32)BIT(8)
>
>  struct stm32_rtc {
>  	struct rtc_device *rtc_dev;
>

Regards,
Amelie