[PATCH v2][net-next] soc: fsl: dpio: Unsigned compared against 0 in qbman_swp_set_irq_coalescing()

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 removing the comparisons altogether as they are incorrect. Zero is
a possible value in either case. Also fix a minor comment typo and update the
2 pr_err() calls to use %u formatting as well as be more precise regarding
the exact error.

Fixes: ed1d2143fee5 ("soc: fsl: dpio: add support for irq coalescing per software portal")
Cc: Ioana Ciornei <ioana.ciornei@nxp.com>
Cc: Roy Pledge <Roy.Pledge@nxp.com>
Cc: Li Yang <redacted>
Cc: linux-kernel@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: netdev@vger.kernel.org
Signed-off-by: Tim Gardner <redacted>
---

v1 - check itp and irq_threshold for 0.
v2 - drop the checks for comparison to 0. Update pr_err() calls with precise language
     about the error.

---
 drivers/soc/fsl/dpio/qbman-portal.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/soc/fsl/dpio/qbman-portal.c b/drivers/soc/fsl/dpio/qbman-portal.c
index d3c58df6240d..3474bf5f88d5 100644
--- a/drivers/soc/fsl/dpio/qbman-portal.c
+++ b/drivers/soc/fsl/dpio/qbman-portal.c

@@ -1816,18 +1816,17 @@ 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 > 4096) {
 		max_holdoff = (p->desc->qman_256_cycles_per_ns * 4096) / 1000;
-		pr_err("irq_holdoff must be between 0..%dus\n", max_holdoff);
+		pr_err("irq_holdoff must be <= %uus\n", max_holdoff);
 		return -EINVAL;
 	}
 
-	if (irq_threshold >= p->dqrr.dqrr_size || irq_threshold < 0) {
-		pr_err("irq_threshold must be between 0..%d\n",
-		       p->dqrr.dqrr_size - 1);
+	if (irq_threshold >= p->dqrr.dqrr_size) {
+		pr_err("irq_threshold must be < %u\n", p->dqrr.dqrr_size - 1);
 		return -EINVAL;
 	}
 

-- 
2.33.1

On Tue, Oct 19, 2021 at 06:19:25AM -0600, Tim Gardner wrote:

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 removing the comparisons altogether as they are incorrect. Zero is
a possible value in either case. Also fix a minor comment typo and update the
2 pr_err() calls to use %u formatting as well as be more precise regarding
the exact error.

Fixes: ed1d2143fee5 ("soc: fsl: dpio: add support for irq coalescing per software portal")
Cc: Ioana Ciornei <ioana.ciornei@nxp.com>
Cc: Roy Pledge <Roy.Pledge@nxp.com>
Cc: Li Yang <redacted>
Cc: linux-kernel@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: netdev@vger.kernel.org
Signed-off-by: Tim Gardner <redacted>

Tested-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>

Thanks,

-Ioana

Hello:

This patch was applied to netdev/net-next.git (master)
by David S. Miller [off-list ref]:

On Tue, 19 Oct 2021 06:19:25 -0600 you wrote:

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        }

[...]

Here is the summary with links:
  - [v2,net-next] soc: fsl: dpio: Unsigned compared against 0 in qbman_swp_set_irq_coalescing()
    https://git.kernel.org/netdev/net-next/c/818a76a55d6e

You are awesome, thank you!
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