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From:   Eliav Farber <farbere@amazon.com>
To:     <jdelvare@suse.com>, <linux@roeck-us.net>, <robh+dt@kernel.org>,
        <p.zabel@pengutronix.de>, <rtanwar@maxlinear.com>,
        <linux-hwmon@vger.kernel.org>, <devicetree@vger.kernel.org>,
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Subject: [PATCH v3 12/19] hwmon: (mr75203) fix voltage equation for negative source input
Date:   Tue, 30 Aug 2022 19:22:05 +0000
Message-ID: <20220830192212.28570-13-farbere@amazon.com>
In-Reply-To: <20220830192212.28570-1-farbere@amazon.com>
References: <20220830192212.28570-1-farbere@amazon.com>
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According to Moortec Embedded Voltage Monitor (MEVM) series 3 data sheet,
the minimum input signal is -100mv and maximum input signal is +1000mv.
When n was small enough, such that PVT_N_CONST * n < PVT_R_CONST it
resulted in n overflowing to a very large number (since n is u32 type).

This change fixes the problem by casting n to long and replacing shift
right with div operation.

Signed-off-by: Eliav Farber <farbere@amazon.com>
---
V3 -> V2:
- Fix equation to support negative values instead of limiting value to
  zero.

 drivers/hwmon/mr75203.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/mr75203.c b/drivers/hwmon/mr75203.c
index 1cd5ff6eacce..d1f090a9baac 100644
--- a/drivers/hwmon/mr75203.c
+++ b/drivers/hwmon/mr75203.c
@@ -222,10 +222,11 @@ static int pvt_read_in(struct device *dev, u32 attr, int channel, long *val)
 			return ret;
 
 		n &= SAMPLE_DATA_MSK;
+
 		/* Convert the N bitstream count into voltage */
 		pre_scaler = pvt->vd[channel].pre_scaler;
-		*val = pre_scaler * (PVT_N_CONST * n - PVT_R_CONST) >>
-			PVT_CONV_BITS;
+		*val = pre_scaler * (PVT_N_CONST * (long)n - PVT_R_CONST) /
+			(1 << PVT_CONV_BITS);
 
 		return 0;
 	default:
-- 
2.37.1