ice: add documentation for FW logging

Add documentation for FW logging in
Documentation/networking/device_drivers/ethernet/intel/ice.rst
Signed-off-by: Paul M Stillwell Jr <paul.m.stillwell.jr@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

Documentation/networking/device_drivers/ethernet/intel/ice.rst

@@ -895,6 +895,147 @@ driver writes raw bytes by the GNSS object to the receiver through i2c. Please
 refer to the hardware GNSS module documentation for configuration details.
 
 
+Firmware (FW) logging
+---------------------
+The driver supports FW logging via the debugfs interface on PF 0 only. The FW
+running on the NIC must support FW logging; if the FW doesn't support FW logging
+the 'fwlog' file will not get created in the ice debugfs directory.
+
+Module configuration
+~~~~~~~~~~~~~~~~~~~~
+Firmware logging is configured on a per module basis. Each module can be set to
+a value independent of the other modules (unless the module 'all' is specified).
+The modules will be instantiated under the 'fwlog/modules' directory.
+
+The user can set the log level for a module by writing to the module file like
+this::
+
+  # echo <log_level> > /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/modules/<module>
+
+where
+
+* log_level is a name as described below. Each level includes the
+  messages from the previous/lower level
+
+      *	none
+      *	error
+      *	warning
+      *	normal
+      *	verbose
+
+* module is a name that represents the module to receive events for. The
+  module names are
+
+      *	general
+      *	ctrl
+      *	link
+      *	link_topo
+      *	dnl
+      *	i2c
+      *	sdp
+      *	mdio
+      *	adminq
+      *	hdma
+      *	lldp
+      *	dcbx
+      *	dcb
+      *	xlr
+      *	nvm
+      *	auth
+      *	vpd
+      *	iosf
+      *	parser
+      *	sw
+      *	scheduler
+      *	txq
+      *	rsvd
+      *	post
+      *	watchdog
+      *	task_dispatch
+      *	mng
+      *	synce
+      *	health
+      *	tsdrv
+      *	pfreg
+      *	mdlver
+      *	all
+
+The name 'all' is special and allows the user to set all of the modules to the
+specified log_level or to read the log_level of all of the modules.
+
+Example usage to configure the modules
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+To set a single module to 'verbose'::
+
+  # echo verbose > /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/modules/link
+
+To set multiple modules then issue the command multiple times::
+
+  # echo verbose > /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/modules/link
+  # echo warning > /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/modules/ctrl
+  # echo none > /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/modules/dcb
+
+To set all the modules to the same value::
+
+  # echo normal > /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/modules/all
+
+To read the log_level of a specific module (e.g. module 'general')::
+
+  # cat /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/modules/general
+
+To read the log_level of all the modules::
+
+  # cat /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/modules/all
+
+Enabling FW log
+~~~~~~~~~~~~~~~
+Configuring the modules indicates to the FW that the configured modules should
+generate events that the driver is interested in, but it **does not** send the
+events to the driver until the enable message is sent to the FW. To do this
+the user can write a 1 (enable) or 0 (disable) to 'fwlog/enable'. An example
+is::
+
+  # echo 1 > /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/enable
+
+Retrieving FW log data
+~~~~~~~~~~~~~~~~~~~~~~
+The FW log data can be retrieved by reading from 'fwlog/data'. The user can
+write any value to 'fwlog/data' to clear the data. The data can only be cleared
+when FW logging is disabled. The FW log data is a binary file that is sent to
+Intel and used to help debug user issues.
+
+An example to read the data is::
+
+  # cat /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/data > fwlog.bin
+
+An example to clear the data is::
+
+  # echo 0 > /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/data
+
+Changing how often the log events are sent to the driver
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The driver receives FW log data from the Admin Receive Queue (ARQ). The
+frequency that the FW sends the ARQ events can be configured by writing to
+'fwlog/nr_messages'. The range is 1-128 (1 means push every log message, 128
+means push only when the max AQ command buffer is full). The suggested value is
+10. The user can see what the value is configured to by reading
+'fwlog/nr_messages'. An example to set the value is::
+
+  # echo 50 > /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/nr_messages
+
+Configuring the amount of memory used to store FW log data
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The driver stores FW log data within the driver. The default size of the memory
+used to store the data is 1MB. Some use cases may require more or less data so
+the user can change the amount of memory that is allocated for FW log data.
+To change the amount of memory then write to 'fwlog/log_size'. The value must be
+one of: 128K, 256K, 512K, 1M, or 2M. FW logging must be disabled to change the
+value. An example of changing the value is::
+
+  # echo 128K > /sys/kernel/debug/ice/0000\:18\:00.0/fwlog/log_size
+
+
 Performance Optimization
 ========================
 Driver defaults are meant to fit a wide variety of workloads, but if further