[PATCH linux dev-4.10 3/3] hwmon: pmbus: core: One-shot retries for failure to set page

[Andrew Jeffery]

Work around the shonky behaviour seen with the MAX31785 where we fail
to set the page register in some circumstances.

There's no real elegant way to do this. We can propagate the error up,
but that forces us to retry the operation way up the call tree in any
number of places. It also forces callers to split out pmbus_set_page()
from the pmbus_{read,write}_{byte,word}_data() functions in order to
differentiate between a failure to set the page and a failure to read a
register (that might not exist, in which case an error is anticiptated).

Cc: Eddie James <eajames at linux.vnet.ibm.com>
Cc: Matt Spinler <mspinler at linux.vnet.ibm.com>
Signed-off-by: Andrew Jeffery <andrew at aj.id.au>
---
 drivers/hwmon/pmbus/pmbus_core.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index 390a7b02b836..d4e959bda491 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -168,7 +168,18 @@ int pmbus_set_page(struct i2c_client *client, u8 page)
 		return 0;
 
 	if (!(data->info->func[page] & PMBUS_PAGE_VIRTUAL)) {
+		dev_dbg(&client->dev, "Want page %u, %u cached\n", page,
+			data->currpage);
+
 		rv = i2c_smbus_write_byte_data(client, PMBUS_PAGE, page);
+		if (rv) {
+			rv = i2c_smbus_write_byte_data(client, PMBUS_PAGE,
+						       page);
+			dev_warn(&client->dev,
+				 "Failed to set page %u, performed one-shot retry %s: %d\n",
+				 page, rv ? "and failed" : "with success", rv);
+		}
+
 		newpage = i2c_smbus_read_byte_data(client, PMBUS_PAGE);
 		if (newpage != page)
 			return -EIO;
-- 
2.11.0