hwmon: (pmbus_core) Do not enable PEC if adapter doesn't (#215)

Currently, for Packet Error Checking (PEC) only the controller
is checked for support. This causes problems on the cisco-8000
platform where a SMBUS transaction errors are observed. This is
because PEC has to be enabled only if both controller and
adapter supports it.

Added code to check PEC capability for adapter and enable it
only if both controller and adapter supports PEC.

Signed-off-by: Madhava Reddy Siddareddygari <msiddare@cisco.com>

patch/cisco-hwmon-pmbus_core-pec-support-check.patch

@@ -0,0 +1,44 @@
+From a3e00e49a8647ea9ba6f08a36c1bf6884f91619a Mon Sep 17 00:00:00 2001
+From: Madhava Reddy Siddareddygari <msiddare@cisco.com>
+Date: Tue, 1 Jun 2021 22:42:41 -0700
+Subject: [PATCH] hwmon: (pmbus_core) Check adapter PEC support
+
+Currently, for Packet Error Checking (PEC) only the controller
+is checked for support. This causes problems on the cisco-8000
+platform where a SMBUS transaction errors are observed. This is
+because PEC has to be enabled only if both controller and
+adapter supports it.
+
+Added code to check PEC capability for adapter and enable it
+only if both controller and adapter supports PEC.
+
+Signed-off-by: Madhava Reddy Siddareddygari <msiddare@cisco.com>
+---
+ drivers/hwmon/pmbus/pmbus_core.c | 10 +++++++---
+ 1 file changed, 7 insertions(+), 3 deletions(-)
+
+diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
+index df4a6de24..2f98b4785 100644
+--- a/drivers/hwmon/pmbus/pmbus_core.c
++++ b/drivers/hwmon/pmbus/pmbus_core.c
+@@ -2082,10 +2082,14 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
+ data->has_status_word = true;
+ }
+
+- /* Enable PEC if the controller supports it */
++ /* Enable PEC if the controller and bus supports it */
+ ret = i2c_smbus_read_byte_data(client, PMBUS_CAPABILITY);
+- if (ret >= 0 && (ret & PB_CAPABILITY_ERROR_CHECK))
+- client->flags |= I2C_CLIENT_PEC;
++ if (ret >= 0 && (ret & PB_CAPABILITY_ERROR_CHECK)) {
++ if (i2c_check_functionality(client->adapter,
++ I2C_FUNC_SMBUS_PEC)) {
++ client->flags |= I2C_CLIENT_PEC;
++ }
++ }
+
+ if (data->info->pages)
+ pmbus_clear_faults(client);
+-- 
+2.26.2
+