Re: [PATCH v3] spi: spi-cadence-quadspi: Fix division by zero warning

[Pratyush Yadav <p.yadav@xxxxxx>]

On 15/07/21 04:21PM, Yoshitaka Ikeda wrote:
> Fix below division by zero warning:
> - Added an if statement because buswidth can be zero, resulting in division by zero.
> - The modified code was based on another driver (atmel-quadspi).
> 
> [    0.795337] Division by zero in kernel.
>    :
> [    0.834051] [<807fd40c>] (__div0) from [<804e1acc>] (Ldiv0+0x8/0x10)
> [    0.839097] [<805f0710>] (cqspi_exec_mem_op) from [<805edb4c>] (spi_mem_exec_op+0x3b0/0x3f8)

Please add a fixes tag.

Fixes: 7512eaf54190 ("spi: cadence-quadspi: Fix dummy cycle calculation when buswidth > 1")

> 
> Signed-off-by: Yoshitaka Ikeda <ikeda@xxxxxxxxxxxx>
> ---
> v2:
> - Fix commit message.
> v3:
> - repost.
> 
>  drivers/spi/spi-cadence-quadspi.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c
> index 7a00346ff9b9..13d1f0ce618e 100644
> --- a/drivers/spi/spi-cadence-quadspi.c
> +++ b/drivers/spi/spi-cadence-quadspi.c
> @@ -307,11 +307,13 @@ static unsigned int cqspi_calc_rdreg(struct cqspi_flash_pdata *f_pdata)
>  
>  static unsigned int cqspi_calc_dummy(const struct spi_mem_op *op, bool dtr)
>  {
> -	unsigned int dummy_clk;
> +	unsigned int dummy_clk = 0;

I think you can just do:

  if (!op->dummy.nbytes)
	return 0;

and leave the rest same.

I don't think we should have to check for buswidth here, even though it 
is the one causing divide-by-zero. Any op with positive dummy nbytes but 
with 0 buswidth is invalid. That should be rejected by the SPI MEM core 
or the supports_op(), so it should never even get here.

>  
> -	dummy_clk = op->dummy.nbytes * (8 / op->dummy.buswidth);
> -	if (dtr)
> -		dummy_clk /= 2;
> +	if (op->dummy.buswidth && op->dummy.nbytes) {
> +		dummy_clk = op->dummy.nbytes * (8 / op->dummy.buswidth);
> +		if (dtr)
> +			dummy_clk /= 2;
> +	}
>  
>  	return dummy_clk;
>  }
> -- 
> 2.32.0

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.