linux-kernel - [PATCH 6.8 624/715] iio: gts-helper: Fix division loop

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Date: Sun, 24 Mar 2024 18:33:23 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Matti Vaittinen <mazziesaccount@...il.com>,
	Subhajit Ghosh <subhajit.ghosh@...aklogic.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Sasha Levin <sashal@...nel.org>
Subject: [PATCH 6.8 624/715] iio: gts-helper: Fix division loop

From: Matti Vaittinen <mazziesaccount@...il.com>

[ Upstream commit bb76cc45dcdfcd962a5994b8fe19ab74fc6c3c3a ]

The loop based 64bit division may run for a long time when dividend is a
lot bigger than the divider. Replace the division loop by the
div64_u64() which implementation may be significantly faster.

Tested-by: Subhajit Ghosh <subhajit.ghosh@...aklogic.com>
Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
Fixes: 38416c28e168 ("iio: light: Add gain-time-scale helpers")
Link: https://lore.kernel.org/r/Zcn-6e-0-nh2WcfU@drtxq0yyyyyyyyyyyyyby-3.rev.dnainternet.fi
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/iio/industrialio-gts-helper.c | 15 +--------------
 1 file changed, 1 insertion(+), 14 deletions(-)

diff --git a/drivers/iio/industrialio-gts-helper.c b/drivers/iio/industrialio-gts-helper.c
index 7653261d2dc2b..b51eb6cb766f3 100644
--- a/drivers/iio/industrialio-gts-helper.c
+++ b/drivers/iio/industrialio-gts-helper.c
@@ -34,24 +34,11 @@
 static int iio_gts_get_gain(const u64 max, const u64 scale)
 {
 	u64 full = max;
-	int tmp = 1;
 
 	if (scale > full || !scale)
 		return -EINVAL;
 
-	if (U64_MAX - full < scale) {
-		/* Risk of overflow */
-		if (full - scale < scale)
-			return 1;
-
-		full -= scale;
-		tmp++;
-	}
-
-	while (full > scale * (u64)tmp)
-		tmp++;
-
-	return tmp;
+	return div64_u64(full, scale);
 }
 
 /**
-- 
2.43.0