[PATCH 4/4] doc: Update description about memmap option in kernel-parameter.txt

[Baoquan He]

In commit 9710f581bb4c ("x86, mm: Let "memmap=" take more entries one time")
memmap was changed to adopt multiple values with comma delimited in
one entry, so update the related description.

And if only specify size value without offset, like memmap=nn[KMG],
memmap behaves equal to mem=nn[KMG], update it too here.

And for memmap=nn[KMG]$ss[KMG], escape character need be added before
'$' for some bootloaders. E.g in grub2, if specified memmap=100M$5G,
actually it passed memmap=100MG to kernel.

Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
---
 Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index facc20a..6789262 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2112,6 +2112,12 @@
 	memmap=nn[KMG]@ss[KMG]
 			[KNL] Force usage of a specific region of memory.
 			Region of memory to be used is from ss to ss+nn.
+			If @ss[KMG] is ommited, it equals to mem=nn[KMG]
+			which limits max address as nn[KMG].
+			Multiple different options can be put into one entry
+			with comma delimited to save space:
+			Example:
+				memmap=100M@2G,100M#3G,1G!1024G
 
 	memmap=nn[KMG]#ss[KMG]
 			[KNL,ACPI] Mark specific memory as ACPI data.
@@ -2124,6 +2130,9 @@
 			         memmap=64K$0x18690000
 			         or
 			         memmap=0x10000$0x18690000
+			Some bootloaders may need escape character before '$',
+			like in grub2, otherwise '$' and the following number
+			will be eaten.
 
 	memmap=nn[KMG]!ss[KMG]
 			[KNL,X86] Mark specific memory as protected.
-- 
2.5.5