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Date:   Sat, 27 Feb 2021 10:34:42 +0100
From:   Wilken Gottwalt <wilken.gottwalt@posteo.net>
To:     linux-kernel@vger.kernel.org
Cc:     Jean Delvare <jdelvare@suse.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Jonathan Corbet <corbet@lwn.net>, linux-hwmon@vger.kernel.org
Subject: [PATCH] hwmon: corsair-psu: update calculation of LINEAR11 values
Message-ID: <YDoSMqFbgoTXyoru@monster.powergraphx.local>
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Changes the way how LINEAR11 values are calculated. The new method
increases the precision of 2-3 digits.

old method:
	corsairpsu-hid-3-1
	Adapter: HID adapter
	v_in:        230.00 V
	v_out +12v:   12.00 V
	v_out +5v:     5.00 V
	v_out +3.3v:   3.00 V
	psu fan:        0 RPM
	vrm temp:     +44.0?C
	case temp:    +37.0?C
	power total: 152.00 W
	power +12v:  112.00 W
	power +5v:    38.00 W
	power +3.3v:   5.00 W
	curr in:          N/A
	curr +12v:     9.00 A
	curr +5v:      7.00 A
	curr +3.3v:  1000.00 mA

new method:
	corsairpsu-hid-3-1
	Adapter: HID adapter
	v_in:        230.00 V
	v_out +12v:   12.16 V
	v_out +5v:     5.01 V
	v_out +3.3v:   3.30 V
	psu fan:        0 RPM
	vrm temp:     +44.5?C
	case temp:    +37.8?C
	power total: 148.00 W
	power +12v:  108.00 W
	power +5v:    37.00 W
	power +3.3v:   4.50 W
	curr in:          N/A
	curr +12v:     9.25 A
	curr +5v:      7.50 A
	curr +3.3v:    1.50 A

Co-developed-by: Jack Doan <me@jackdoan.com>
Signed-off-by: Jack Doan <me@jackdoan.com>
Signed-off-by: Wilken Gottwalt <wilken.gottwalt@posteo.net>
---
 drivers/hwmon/corsair-psu.c | 30 ++++++++----------------------
 1 file changed, 8 insertions(+), 22 deletions(-)

diff --git a/drivers/hwmon/corsair-psu.c b/drivers/hwmon/corsair-psu.c
index 99494056f4bd..b0953eeeb2d3 100644
--- a/drivers/hwmon/corsair-psu.c
+++ b/drivers/hwmon/corsair-psu.c
@@ -119,27 +119,13 @@ struct corsairpsu_data {
 };
 
 /* some values are SMBus LINEAR11 data which need a conversion */
-static int corsairpsu_linear11_to_int(const int val)
+static int corsairpsu_linear11_to_int(const u16 val, const int scale)
 {
-	int exp = (val & 0xFFFF) >> 0x0B;
-	int mant = val & 0x7FF;
-	int i;
-
-	if (exp > 0x0F)
-		exp -= 0x20;
-	if (mant > 0x3FF)
-		mant -= 0x800;
-	if ((mant & 0x01) == 1)
-		++mant;
-	if (exp < 0) {
-		for (i = 0; i < -exp; ++i)
-			mant /= 2;
-	} else {
-		for (i = 0; i < exp; ++i)
-			mant *= 2;
-	}
+	const int exp = ((s16)val) >> 11;
+	const int mant = (((s16)(val & 0x7ff)) << 5) >> 5;
+	const int result = mant * scale;
 
-	return mant;
+	return (exp >= 0) ? (result << exp) : (result >> -exp);
 }
 
 static int corsairpsu_usb_cmd(struct corsairpsu_data *priv, u8 p0, u8 p1, u8 p2, void *data)
@@ -249,14 +235,14 @@ static int corsairpsu_get_value(struct corsairpsu_data *priv, u8 cmd, u8 rail, l
 	case PSU_CMD_RAIL_AMPS:
 	case PSU_CMD_TEMP0:
 	case PSU_CMD_TEMP1:
-		*val = corsairpsu_linear11_to_int(tmp & 0xFFFF) * 1000;
+		*val = corsairpsu_linear11_to_int(tmp & 0xFFFF, 1000);
 		break;
 	case PSU_CMD_FAN:
-		*val = corsairpsu_linear11_to_int(tmp & 0xFFFF);
+		*val = corsairpsu_linear11_to_int(tmp & 0xFFFF, 1);
 		break;
 	case PSU_CMD_RAIL_WATTS:
 	case PSU_CMD_TOTAL_WATTS:
-		*val = corsairpsu_linear11_to_int(tmp & 0xFFFF) * 1000000;
+		*val = corsairpsu_linear11_to_int(tmp & 0xFFFF, 1000000);
 		break;
 	case PSU_CMD_TOTAL_UPTIME:
 	case PSU_CMD_UPTIME:
-- 
2.30.1