linux-kernel - Re: [PATCH] soundwire: qcom: use signed variable for error return

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Message-ID: <9cdef4e9-a38a-6c77-1b23-739f85384b12@linux.intel.com>
Date:   Wed, 31 Mar 2021 09:41:24 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Vinod Koul <vkoul@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        linux-arm-msm@...r.kernel.org, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] soundwire: qcom: use signed variable for error return



On 3/31/21 2:21 AM, 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@...el.com>
> Signed-off-by: Vinod Koul <vkoul@...nel.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;

it's not great to store negative error codes with s8. That works in this 
specific case because the function only returns -EINVAL.

We actually have zero occurrences of s8 in the drivers/soundwire/ code.

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