linux-kernel - [PATCH v3] spi: fix the divide by 0 error when calculating xfer waiting time

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Message-Id: <1609723749-3557-1-git-send-email-yilun.xu@intel.com>
Date:   Mon,  4 Jan 2021 09:29:09 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     broonie@...nel.org, linux-spi@...r.kernel.org
Cc:     trix@...hat.com, lgoncalv@...hat.com, yilun.xu@...el.com,
        hao.wu@...el.com, matthew.gerlach@...ux.intel.com,
        russell.h.weight@...el.com, linux-kernel@...r.kernel.org
Subject: [PATCH v3] spi: fix the divide by 0 error when calculating xfer waiting time

The xfer waiting time is the result of xfer->len / xfer->speed_hz. This
patch makes the assumption of 100khz xfer speed if the xfer->speed_hz is
not assigned and stays 0. This avoids the divide by 0 issue and ensures
a reasonable tolerant waiting time.

Signed-off-by: Xu Yilun <yilun.xu@...el.com>
---
v2: use the normal conditional statement instead of the ternery operator
    change the default xfer speed from 1khz to 100khz
v3: fix the commit message
---
 drivers/spi/spi.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 51d7c00..aacae88 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1108,6 +1108,7 @@ static int spi_transfer_wait(struct spi_controller *ctlr,
 {
 	struct spi_statistics *statm = &ctlr->statistics;
 	struct spi_statistics *stats = &msg->spi->statistics;
+	u32 speed_hz = xfer->speed_hz;
 	unsigned long long ms;
 
 	if (spi_controller_is_slave(ctlr)) {
@@ -1116,8 +1117,11 @@ static int spi_transfer_wait(struct spi_controller *ctlr,
 			return -EINTR;
 		}
 	} else {
+		if (!speed_hz)
+			speed_hz = 100000;
+
 		ms = 8LL * 1000LL * xfer->len;
-		do_div(ms, xfer->speed_hz);
+		do_div(ms, speed_hz);
 		ms += ms + 200; /* some tolerance */
 
 		if (ms > UINT_MAX)
-- 
2.7.4