[PATCH] hwmon: (pmbus) More stringent checking of VOUT_MODE register

[PATCH] hwmon: (pmbus) More stringent checking of VOUT_MODE register

[Guenter Roeck]

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@cisco.com>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.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

Re: [PATCH] hwmon: (pmbus) More stringent checking of VOUT_MODE register

[Greg Schnorr]

Looks good, tested and works on one such VOUT_MODE poor design...

On 3/1/11 9:32 PM, "Guenter Roeck" <guenter.roeck@ericsson.com> wrote:

> 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@cisco.com>
> Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Acked-by: Greg Schnorr <gschnorr@cisco.com>

Re: [PATCH] hwmon: (pmbus) More stringent checking of VOUT_MODE register

[Guenter Roeck]

On Mon, Mar 07, 2011 at 04:44:43PM -0500, Greg Schnorr wrote:
> Looks good, tested and works on one such VOUT_MODE poor design...
> 
> On 3/1/11 9:32 PM, "Guenter Roeck" <guenter.roeck@ericsson.com> wrote:
> 
> > 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@cisco.com>
> > Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
> Acked-by: Greg Schnorr <gschnorr@cisco.com>
> 
Thanks!

Guenter