Documentation/admin-guide: kernel-parameters: Update nohlt section

Update the documentation regarding "nohlt" and indicate that it is not
only for bugs, but can be useful to disable the architecture specific
sleep instructions. ARM, ARM64, SuperH and Microblaze all use
CONFIG_GENERIC_IDLE_POLL_SETUP which takes care of honoring the
"hlt"/"nohlt" parameters.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20210209172349.2249596-1-f.fainelli@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Author: ffainelli

Documentation/admin-guide/kernel-parameters.txt

@@ -3266,9 +3266,14 @@
 			parameter, xsave area per process might occupy more
 			memory on xsaves enabled systems.
 
-	nohlt		[BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
-			wfi(ARM) instruction doesn't work correctly and not to
-			use it. This is also useful when using JTAG debugger.
+	nohlt		[ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait
+			in do_idle() and not use the arch_cpu_idle()
+			implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
+			to be effective. This is useful on platforms where the
+			sleep(SH) or wfi(ARM,ARM64) instructions do not work
+			correctly or when doing power measurements to evalute
+			the impact of the sleep instructions. This is also
+			useful when using JTAG debugger.
 
 	no_file_caps	Tells the kernel not to honor file capabilities.  The
 			only way then for a file to be executed with privilege