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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Yoshitaka Ikeda <ikeda@nskint.co.jp>,
        Pratyush Yadav <p.yadav@ti.com>,
        Mark Brown <broonie@kernel.org>
Subject: [PATCH 5.13 222/223] spi: spi-cadence-quadspi: Fix division by zero warning - try2
Date:   Mon, 26 Jul 2021 17:40:14 +0200
Message-Id: <20210726153853.444570566@linuxfoundation.org>
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From: Yoshitaka Ikeda <ikeda@nskint.co.jp>

commit 0e85ee897858b1c7a5de53f496d016899d9639c5 upstream.

Fix below division by zero warning:
- The reason for dividing by zero is because the dummy bus width is zero,
  but if the dummy n bytes is zero, it indicates that there is no data transfer,
  so we can just return zero without doing any calculations.

[    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)

Fixes: 7512eaf54190 ("spi: cadence-quadspi: Fix dummy cycle calculation when buswidth > 1")
Signed-off-by: Yoshitaka Ikeda <ikeda@nskint.co.jp>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/92eea403-9b21-2488-9cc1-664bee760c5e@nskint.co.jp
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/spi/spi-cadence-quadspi.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/spi/spi-cadence-quadspi.c
+++ b/drivers/spi/spi-cadence-quadspi.c
@@ -309,6 +309,9 @@ static unsigned int cqspi_calc_dummy(con
 {
 	unsigned int dummy_clk;
 
+	if (!op->dummy.nbytes)
+		return 0;
+
 	dummy_clk = op->dummy.nbytes * (8 / op->dummy.buswidth);
 	if (dtr)
 		dummy_clk /= 2;