[PATCH v2 2/2] docs: hwmon: Update driver documentation for debugfs

[Grant Peltier]

Add usage details for the two new debugfs endpoints for 2nd Gen devices:
read_black_box and write_config

Signed-off-by: Grant Peltier <grantpeltier93@xxxxxxxxx>
---
 Documentation/hwmon/isl68137.rst | 34 +++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/Documentation/hwmon/isl68137.rst b/Documentation/hwmon/isl68137.rst
index 0e71b22047f8..c5f7b2981db6 100644
--- a/Documentation/hwmon/isl68137.rst
+++ b/Documentation/hwmon/isl68137.rst
@@ -423,7 +423,8 @@ Beyond the normal sysfs pmbus attributes, the driver exposes a control attribute
 for the ISL68137.
 
 For 2nd generation Renesas digital multiphase voltage regulators, only the
-normal sysfs pmbus attributes are supported.
+normal sysfs pmbus attributes are supported. However, 2nd generation devices do
+have additional debugfs features which are detailed below.
 
 ISL68137 sysfs attributes
 -------------------------
@@ -603,3 +604,34 @@ temp[1-7]_crit_alarm	Chip temperature critical high alarm
 temp[1-7]_max		Maximum temperature
 temp[1-7]_max_alarm	Chip temperature high alarm
 ======================= ==========================================
+
+debugfs features (Gen 2 ONLY)
+-----------------------------
+
+If you have debugfs enabled, two file endpoints will be created under
+`/sys/kernel/debug/pmbus/<device-id>` when you instantiate a 2nd generation
+device: `read_black_box` and `write_config`.
+
+`read_black_box` is a read-only file. When read, the driver will attempt to read
+the contents of the device's fault recording RAM segment called "Black Box". The
+RAM segment is then printed to the file as hex formatted strings. For easier
+consumption, the 128-byte segment is broken up into 32 4-byte little-endian
+lines (i.e. each line starts with the least significant byte). See your device's
+datasheet for information regarding how to parse the data.
+
+.. warning::
+    When using `write_config`, only use hex files as they are exported from the
+    Renesas Power Navigator application:
+    https://www.renesas.com/us/en/products/power-management/digital-power/powernavigator.html
+
+`write_config` is a write-only file. This endpoint expects the contents of a
+configuration hex file specific to your device exactly as it is exported from
+the Renesas Power Navigator application. When this endpoint is written to, the
+driver will attempt to write the contents of the file down to one or more of the
+device's NVM slots and will return a standard error code if any part of the
+process fails. Be careful when using this feature as writing an unstable
+configuration to your device may may cause it to misbehave. Each device also has
+a fixed number of NVM writes allowed. Consult the datasheet for your device for
+more information about NVM configuration options. Finally, note that you will
+have to power cycle your device in order for NVM configuration changes to take
+effect.
-- 
2.20.1