linux-kernel - Re: [PATCH 4/5] mfd: sprd-sc27xx-spi: Fix divide by zero when allocating register offset/mask

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Date:   Mon, 29 Jun 2020 15:06:44 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Baolin Wang <baolin.wang7@...il.com>,
        Orson Zhai <orsonzhai@...il.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Chunyan Zhang <zhang.lyra@...il.com>
Subject: Re: [PATCH 4/5] mfd: sprd-sc27xx-spi: Fix divide by zero when
 allocating register offset/mask

On Mon, Jun 29, 2020 at 01:32:14PM +0100, Lee Jones wrote:
> Since ddata->irqs[] is already zeroed when allocated by devm_kcalloc() and
> dividing 0 by anything is still 0, there is no need to re-assign
> ddata->irqs[i].* values.  Instead, it should be safe to begin at 1.
> 
> This fixes the following W=1 warning:
> 
>  drivers/mfd/sprd-sc27xx-spi.c:255 sprd_pmic_probe() debug: sval_binop_unsigned: divide by zero
> 
> Cc: Orson Zhai <orsonzhai@...il.com>
> Cc: Baolin Wang <baolin.wang7@...il.com>
> Cc: Chunyan Zhang <zhang.lyra@...il.com>
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---
>  drivers/mfd/sprd-sc27xx-spi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mfd/sprd-sc27xx-spi.c b/drivers/mfd/sprd-sc27xx-spi.c
> index c305e941e435c..694a7d429ccff 100644
> --- a/drivers/mfd/sprd-sc27xx-spi.c
> +++ b/drivers/mfd/sprd-sc27xx-spi.c
> @@ -251,7 +251,7 @@ static int sprd_pmic_probe(struct spi_device *spi)
>  		return -ENOMEM;
>  
>  	ddata->irq_chip.irqs = ddata->irqs;
> -	for (i = 0; i < pdata->num_irqs; i++) {
> +	for (i = 1; i < pdata->num_irqs; i++) {
>  		ddata->irqs[i].reg_offset = i / pdata->num_irqs;
>  		ddata->irqs[i].mask = BIT(i % pdata->num_irqs);
>  	}

This doesn't look right either.

First, the loop is never executed if num_irqs is zero.

Second, the current code looks bogus too as reg_offset is always set to
zero and mask to BIT(i)...

Johan