--- zzzz-none-000/linux-3.10.107/Documentation/pps/pps.txt	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/Documentation/pps/pps.txt	2021-02-04 17:41:59.000000000 +0000
@@ -66,6 +66,21 @@
 into files /dev/pps0, /dev/pps1, etc..
 
 
+PPS with USB to serial devices
+------------------------------
+
+It is possible to grab the PPS from an USB to serial device. However,
+you should take into account the latencies and jitter introduced by
+the USB stack. Users has reported clock instability around +-1ms when
+synchronized with PPS through USB. This isn't suited for time server
+synchronization.
+
+If your device doesn't report PPS, you can check that the feature is
+supported by its driver. Most of the time, you only need to add a call
+to usb_serial_handle_dcd_change after checking the DCD status (see
+ch341 and pl2303 examples).
+
+
 Coding example
 --------------
 
@@ -110,7 +125,7 @@
 (pps_ktimer_echo(), passing to it the "ptr" pointer) if the user
 asked for that... etc..
 
-Please see the file drivers/pps/clients/ktimer.c for example code.
+Please see the file drivers/pps/clients/pps-ktimer.c for example code.
 
 
 SYSFS support
@@ -151,7 +166,7 @@
 
 In order to test the PPS support even without specific hardware you can use
 the ktimer driver (see the client subsection in the PPS configuration menu)
-and the userland tools provided into Documentaion/pps/ directory.
+and the userland tools provided in the Documentation/pps/ directory.
 
 Once you have enabled the compilation of ktimer just modprobe it (if
 not statically compiled):