linux-kernel - Re: [PATCH][linux-next] soc: fsl: dpio: Unsigned compared against 0 in

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Message-Id: <20211019090855.246625-1-ioana.ciornei@nxp.com>
Date:   Tue, 19 Oct 2021 12:08:55 +0300
From:   Ioana Ciornei <ioana.ciornei@....com>
To:     tim.gardner@...onical.com
Cc:     linux-arm-kernel@...ts.infradead.org, leoyang.li@....com,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH][linux-next] soc: fsl: dpio: Unsigned compared against 0 in

> 
> Subject: [PATCH][linux-next] soc: fsl: dpio: Unsigned compared against 0 in
> 
> Coverity complains of unsigned compare against 0. There are 2 cases in
> this function:
> 
> 1821        itp = (irq_holdoff * 1000) / p->desc->qman_256_cycles_per_ns;
> 
> CID 121131 (#1 of 1): Unsigned compared against 0 (NO_EFFECT)
> unsigned_compare: This less-than-zero comparison of an unsigned value is never true. itp < 0U.
> 1822        if (itp < 0 || itp > 4096) {
> 1823                max_holdoff = (p->desc->qman_256_cycles_per_ns * 4096) / 1000;
> 1824                pr_err("irq_holdoff must be between 0..%dus\n", max_holdoff);
> 1825                return -EINVAL;
> 1826        }
> 1827
>     	unsigned_compare: This less-than-zero comparison of an unsigned value is never true. irq_threshold < 0U.
> 1828        if (irq_threshold >= p->dqrr.dqrr_size || irq_threshold < 0) {
> 1829                pr_err("irq_threshold must be between 0..%d\n",
> 1830                       p->dqrr.dqrr_size - 1);
> 1831                return -EINVAL;
> 1832        }
> 
> Fix this by checking for 0. Also fix a minor comment typo.
> 
> Fixes ed1d2143fee53755ec601eb4d48a337a93933f71 ("soc: fsl: dpio: add support for
> irq coalescing per software portal")

I think this should be formatted as following:

Fixes: ed1d2143fee5 ("soc: fsl: dpio: add support for irq coalescing per software portal")

> 
> Cc: Roy Pledge <Roy.Pledge@....com>
> Cc: Li Yang <leoyang.li@....com>
> Cc: linux-kernel@...r.kernel.org
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: linux-arm-kernel@...ts.infradead.org
> Signed-off-by: Tim Gardner <tim.gardner@...onical.com>
> ---
> 
> I'm not 100% sure this is the right way to fix the warning, but according to the
> pr_err() comments these values should never be 0.

These threshold values can be 0, the pr_err comment tries to say that those are
the ranges, 0 and the maximum included.

> 
> ---
>  drivers/soc/fsl/dpio/qbman-portal.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/soc/fsl/dpio/qbman-portal.c b/drivers/soc/fsl/dpio/qbman-portal.c
> index d3c58df6240d..b768a14bb271 100644
> --- a/drivers/soc/fsl/dpio/qbman-portal.c
> +++ b/drivers/soc/fsl/dpio/qbman-portal.c
> @@ -1816,16 +1816,16 @@ int qbman_swp_set_irq_coalescing(struct qbman_swp *p, u32 irq_threshold,
>  	u32 itp, max_holdoff;
>  
>  	/* Convert irq_holdoff value from usecs to 256 QBMAN clock cycles
> -	 * increments. This depends to the QBMAN internal frequency.
> +	 * increments. This depends on the QBMAN internal frequency.
>  	 */
>  	itp = (irq_holdoff * 1000) / p->desc->qman_256_cycles_per_ns;
> -	if (itp < 0 || itp > 4096) {
> +	if (!itp || itp > 4096) {
>  		max_holdoff = (p->desc->qman_256_cycles_per_ns * 4096) / 1000;
>  		pr_err("irq_holdoff must be between 0..%dus\n", max_holdoff);
>  		return -EINVAL;
>  	}
>  
> -	if (irq_threshold >= p->dqrr.dqrr_size || irq_threshold < 0) {
> +	if (irq_threshold >= p->dqrr.dqrr_size || !irq_threshold) {
>  		pr_err("irq_threshold must be between 0..%d\n",
>  		       p->dqrr.dqrr_size - 1);
>  		return -EINVAL;
> 

These 'value < 0' checks should be removed all together. Somehow I missed that
those are unsigned values.

Anyhow, thanks a lot that you spotted this.

Could you please sent the v2 towards the net-next tree since that's the tree
that adds the fixed patch?

Thanks.

-Ioana