[3.13.y-ckt stable] Patch "hwmon: (mcp3021) Fix broken output scaling" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    hwmon: (mcp3021) Fix broken output scaling

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt24.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 151e9e061556fb0e3dfa53c5a95435c6ad243367 Mon Sep 17 00:00:00 2001
From: "Stevens, Nick" <Nick.Stevens at digi.com>
Date: Wed, 1 Jul 2015 16:07:41 +0000
Subject: hwmon: (mcp3021) Fix broken output scaling

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 <Nick.Stevens at digi.com>
[Guenter Roeck: Dropped unnecessary value check]
Signed-off-by: Guenter Roeck <linux at roeck-us.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/hwmon/mcp3021.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/drivers/hwmon/mcp3021.c b/drivers/hwmon/mcp3021.c
index d219c06..972444a 100644
--- a/drivers/hwmon/mcp3021.c
+++ b/drivers/hwmon/mcp3021.c
@@ -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_client *client)

 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_client *client,
 		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;
 	}

--
1.9.1