linux-kernel - [PATCH 2/2] spi: fix the divide by 0 error when calculating xfer waiting time

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Message-Id: <1609219662-27057-3-git-send-email-yilun.xu@intel.com>
Date:   Tue, 29 Dec 2020 13:27:42 +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 2/2] 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, but
when the following patch is merged,

commit 9326e4f1e5dd ("spi: Limit the spi device max speed to controller's max speed")

the xfer->speed_hz may always be clamped to 0 if the controller doesn't
provide its max_speed_hz. There may be no hardware indication of the
max_speed_hz so the controller driver leaves it, but exception happens
when it tries to do irq mode transfer.

This patch makes the assumption of 1khz xfer speed if the xfer->speed_hz
is not assigned. This avoids the divide by 0 issue and ensures a
reasonable tolerant waiting time.

Signed-off-by: Xu Yilun <yilun.xu@...el.com>
---
 drivers/spi/spi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 51d7c00..2f3c2c9 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1109,6 +1109,7 @@ static int spi_transfer_wait(struct spi_controller *ctlr,
 	struct spi_statistics *statm = &ctlr->statistics;
 	struct spi_statistics *stats = &msg->spi->statistics;
 	unsigned long long ms;
+	u32 speed_hz;
 
 	if (spi_controller_is_slave(ctlr)) {
 		if (wait_for_completion_interruptible(&ctlr->xfer_completion)) {
@@ -1116,8 +1117,9 @@ static int spi_transfer_wait(struct spi_controller *ctlr,
 			return -EINTR;
 		}
 	} else {
+		speed_hz = xfer->speed_hz ? : 1000;
 		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