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Date:   Wed, 31 Mar 2021 11:24:13 -0500
From:   Bjorn Andersson <bjorn.andersson@linaro.org>
To:     Vinod Koul <vkoul@kernel.org>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Bard Liao <yung-chuan.liao@linux.intel.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>,
        Sanyog Kale <sanyog.r.kale@intel.com>,
        linux-arm-msm@vger.kernel.org, alsa-devel@alsa-project.org,
        linux-kernel@vger.kernel.org, kernel test robot <lkp@intel.com>
Subject: Re: [PATCH] soundwire: qcom: use signed variable for error return
Message-ID: <20210331162413.GJ904837@yoga>
References: <20210331072111.2945945-1-vkoul@kernel.org>
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In-Reply-To: <20210331072111.2945945-1-vkoul@kernel.org>
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On Wed 31 Mar 02:21 CDT 2021, Vinod Koul wrote:

> We get warning for using a unsigned variable being compared to less than
> zero. The comparison is correct as it checks for errors from previous
> call to qcom_swrm_get_alert_slave_dev_num(), so we should use a signed
> variable instead.
> 
> drivers/soundwire/qcom.c: qcom_swrm_irq_handler() warn: impossible
> condition '(devnum < 0) => (0-255 < 0)'
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Vinod Koul <vkoul@kernel.org>
> ---
>  drivers/soundwire/qcom.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/soundwire/qcom.c b/drivers/soundwire/qcom.c
> index b08ecb9b418c..55ed133c6704 100644
> --- a/drivers/soundwire/qcom.c
> +++ b/drivers/soundwire/qcom.c
> @@ -428,7 +428,7 @@ static irqreturn_t qcom_swrm_irq_handler(int irq, void *dev_id)
>  	struct qcom_swrm_ctrl *swrm = dev_id;
>  	u32 value, intr_sts, intr_sts_masked, slave_status;
>  	u32 i;
> -	u8 devnum = 0;
> +	s8 devnum = 0;

At least in today's linux-next qcom_swrm_get_alert_slave_dev_num()
returns an int and the code only checks to see if this is negative.  So
it seems like making this a full int ensures there's no truncation etc.

And at least as written today there's no need to initialize the
variable.

Regards,
Bjorn

>  	int ret = IRQ_HANDLED;
>  
>  	swrm->reg_read(swrm, SWRM_INTERRUPT_STATUS, &intr_sts);
> -- 
> 2.26.3
>