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Patch "hwmon: (mcp3021) Fix broken output scaling" has been added to the 3.10-stable tree

PATCH [email protected] 1 participant 1 message Jul 31, 2015

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This is a note to let you know that I've just added the patch titled

hwmon: (mcp3021) Fix broken output scaling

to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
hwmon-mcp3021-fix-broken-output-scaling.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 347d7e45bd09ce09cbc30d5cea9de377eb22f55c Mon Sep 17 00:00:00 2001

From: "Stevens, Nick" <[email protected]>
Date: Wed, 1 Jul 2015 16:07:41 +0000
Subject: hwmon: (mcp3021) Fix broken output scaling

From: "Stevens, Nick" <[email protected]>

commit 347d7e45bd09ce09cbc30d5cea9de377eb22f55c upstream.

The mcp3021 scaling code is dividing the VDD (full-scale) value in millivolts by the A2D resolution to obtain the scaling factor. When VDD is 3300mV (the standard value) and the resolution is 12-bit (4096 divisions), the result is a scale factor of 3300/4096, which is always one. Effectively, the raw A2D reading is always being returned because no scaling is applied.

This patch fixes the issue and simplifies the register-to-volts calculation, removing the unneeded "output_scale" struct member.

Signed-off-by Nick Stevens <[email protected]>
[Guenter Roeck: Dropped unnecessary value check]
Signed-off-by Guenter Roeck <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 drivers/hwmon/mcp3021.c |   14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)
drivers/hwmon/mcp3021.c +1 -13
@@ -31,14 +31,11 @@
 /* output format */
 #define MCP3021_SAR_SHIFT	2
 #define MCP3021_SAR_MASK	0x3ff
-
 #define MCP3021_OUTPUT_RES	10	/* 10-bit resolution */
-#define MCP3021_OUTPUT_SCALE	4
 
 #define MCP3221_SAR_SHIFT	0
 #define MCP3221_SAR_MASK	0xfff
 #define MCP3221_OUTPUT_RES	12	/* 12-bit resolution */
-#define MCP3221_OUTPUT_SCALE	1
 
 enum chips {
 	mcp3021,

@@ -54,7 +51,6 @@ struct mcp3021_data {
 	u16 sar_shift;
 	u16 sar_mask;
 	u8 output_res;
-	u8 output_scale;
 };
 
 static int mcp3021_read16(struct i2c_client *client)

@@ -84,13 +80,7 @@ static int mcp3021_read16(struct i2c_cli
 
 static inline u16 volts_from_reg(struct mcp3021_data *data, u16 val)
 {
-	if (val == 0)
-		return 0;
-
-	val = val * data->output_scale - data->output_scale / 2;
-
-	return val * DIV_ROUND_CLOSEST(data->vdd,
-			(1 << data->output_res) * data->output_scale);
+	return DIV_ROUND_CLOSEST(data->vdd * val, 1 << data->output_res);
 }
 
 static ssize_t show_in_input(struct device *dev, struct device_attribute *attr,

@@ -132,14 +122,12 @@ static int mcp3021_probe(struct i2c_clie
 		data->sar_shift = MCP3021_SAR_SHIFT;
 		data->sar_mask = MCP3021_SAR_MASK;
 		data->output_res = MCP3021_OUTPUT_RES;
-		data->output_scale = MCP3021_OUTPUT_SCALE;
 		break;
 
 	case mcp3221:
 		data->sar_shift = MCP3221_SAR_SHIFT;
 		data->sar_mask = MCP3221_SAR_MASK;
 		data->output_res = MCP3221_OUTPUT_RES;
-		data->output_scale = MCP3221_OUTPUT_SCALE;
 		break;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-3.10/hwmon-mcp3021-fix-broken-output-scaling.patch