[PATCH 10/15] iio: light: tsl2591: don't divide by zero with low gain

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Josef Bacik <josef@toxicpanda.com>

The number of counts per lux is the integration time in milliseconds times
the gain, divided by 408.  With the low gain, which is 1, and an
integration time of 100 to 400 ms, that is 0 in integer arithmetic, and
each read of the illuminance divides by zero.

In that case, multiply by the coefficient and divide by the product
instead.  The result of the other settings does not change.

Fixes: 2335f0d7c790 ("iio: light: Added AMS tsl2591 driver implementation")
Cc: stable <stable@kernel.org>
Cc: David Lechner <dlechner@baylibre.com>
Cc: "Nuno Sá" <nuno.sa@analog.com>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Lucas Rabaquim <lucas.rabaquim@usp.br>
Cc: Matheus Silveira <matheus.feitosa@usp.br>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Stepan Ionichev <sozdayvek@gmail.com>
Cc: Joe Sandom <joe.g.sandom@gmail.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/iio/light/tsl2591.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/light/tsl2591.c b/drivers/iio/light/tsl2591.c
index 286dc09e170f..773b50c17e71 100644
--- a/drivers/iio/light/tsl2591.c
+++ b/drivers/iio/light/tsl2591.c
@@ -16,6 +16,7 @@
 #include <linux/interrupt.h>
 #include <linux/iopoll.h>
 #include <linux/kernel.h>
+#include <linux/math64.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/pm_runtime.h>
@@ -424,8 +425,13 @@ static int tsl2591_read_channel_data(struct iio_dev *indio_dev,
 		}
 
 		/* Calculate lux value */
-		lux = ((als_ch0 - als_ch1) *
-		       (1000 - ((als_ch1 * 1000) / als_ch0))) / counts_per_lux;
+		lux = (als_ch0 - als_ch1) *
+		      (1000 - ((als_ch1 * 1000) / als_ch0));
+		if (counts_per_lux)
+			lux /= counts_per_lux;
+		else	/* Less than one count per lux */
+			lux = div_s64((s64)lux * TSL2591_LUX_COEFFICIENT,
+				      int_time_fval * gain_multi);
 
 		dev_dbg(&client->dev, "Raw lux calculation: %d\n", lux);
 

-- 
2.56.0