linux-kernel - [PATCH] hwmon: (pmbus) More stringent checking of VOUT

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Message-ID: <1299043940-22798-1-git-send-email-guenter.roeck@ericsson.com>
Date:	Tue, 1 Mar 2011 21:32:20 -0800
From:	Guenter Roeck <guenter.roeck@...csson.com>
To:	Jean Delvare <khali@...ux-fr.org>
CC:	Jonathan Cameron <kernel@...23.retrosnub.co.uk>,
	Randy Dunlap <rdunlap@...otime.net>,
	Greg Schnorr <gschnorr@...co.com>, <lm-sensors@...sensors.org>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Guenter Roeck <guenter.roeck@...csson.com>
Subject: [PATCH] hwmon: (pmbus) More stringent checking of VOUT_MODE register

Some PMBus chips do not support the VOUT_MODE register. To make matters worse,
such chips may not return an error when reading the register either, but instead
return 0xff.

Check if the register exists using pmbus_check_byte_register() before reading
its value. In addition, validate the returned value and ignore it if it is 0xff
(which is invalid).

Reported-by: Greg Schnorr <gschnorr@...co.com>
Signed-off-by: Guenter Roeck <guenter.roeck@...csson.com>
---
 drivers/hwmon/pmbus_core.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/pmbus_core.c b/drivers/hwmon/pmbus_core.c
index 0edab1c..b7c64ba 100644
--- a/drivers/hwmon/pmbus_core.c
+++ b/drivers/hwmon/pmbus_core.c
@@ -1426,10 +1426,11 @@ static void pmbus_find_attributes(struct i2c_client *client,
 static int pmbus_identify_common(struct i2c_client *client,
 				 struct pmbus_data *data)
 {
-	int vout_mode, exponent;
+	int vout_mode = -1, exponent;
 
-	vout_mode = pmbus_read_byte_data(client, 0, PMBUS_VOUT_MODE);
-	if (vout_mode >= 0) {
+	if (pmbus_check_byte_register(client, 0, PMBUS_VOUT_MODE))
+		vout_mode = pmbus_read_byte_data(client, 0, PMBUS_VOUT_MODE);
+	if (vout_mode >= 0 && vout_mode != 0xff) {
 		/*
 		 * Not all chips support the VOUT_MODE command,
 		 * so a failure to read it is not an error.
-- 
1.7.3.1

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