From: Mike Rapoport <rppt@linux.ibm.com>

The existing description of mem= does not cover all the cases and
differences between how architectures treat it.

Extend the description to match the code.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
v1: https://lore.kernel.org/all/20220309122446.1118738-1-rppt@kernel.org
* drop clumsy and redundant paragraph about Hexagon

 .../admin-guide/kernel-parameters.txt          | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f5a27f067db9..40cd4136331b 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2834,6 +2834,13 @@
 			2 when the kernel is not able to see the whole system memory;
 			3 memory that lies after 'mem=' boundary is excluded from
 			 the hypervisor, then assigned to KVM guests.
+			4 to limit the memory available for kdump kernel.
+
+			[ARC,MICROBLAZE] - the limit applies only to low memory,
+			high memory is not affected.
+
+			[ARM64] - only limits memory covered by the linear
+			mapping. The NOMAP regions are not affected.
 
 			[X86] Work as limiting max address. Use together
 			with memmap= to avoid physical address space collisions.
@@ -2844,6 +2851,17 @@
 			in above case 3, memory may need be hot added after boot
 			if system memory of hypervisor is not sufficient.
 
+	mem=nn[KMG]@ss[KMG]
+			[ARM,MIPS] - override the memory layout reported by
+			firmware.
+			Define a memory region of size nn[KMG] starting at
+			ss[KMG].
+			Multiple different regions can be specified with
+			multiple mem= parameters on the command line.
+
+	mem=nn[KMG]	[HEXAGON] Set the memory size.
+			Must be specified, otherwise memory size will be 0.
+
 	mem=nopentium	[BUGS=X86-32] Disable usage of 4MB pages for kernel
 			memory.
 
-- 
2.34.1

On Wed, 9 Mar 2022, Mike Rapoport wrote:

> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> The existing description of mem= does not cover all the cases and
> differences between how architectures treat it.
> 
> Extend the description to match the code.

 This:

> +	mem=nn[KMG]	[HEXAGON] Set the memory size.
> +			Must be specified, otherwise memory size will be 0.
> +

I guess would better be folded into the other `mem=nn[KMG]' description 
above, possibly between [ARM64] and [X86] so as to keep the order roughly 
alphabetic.

  Maciej

On Wed, Mar 09, 2022 at 06:13:14PM +0000, Maciej W. Rozycki wrote:
> On Wed, 9 Mar 2022, Mike Rapoport wrote:
> 
> > From: Mike Rapoport <rppt@linux.ibm.com>
> > 
> > The existing description of mem= does not cover all the cases and
> > differences between how architectures treat it.
> > 
> > Extend the description to match the code.
> 
>  This:
> 
> > +	mem=nn[KMG]	[HEXAGON] Set the memory size.
> > +			Must be specified, otherwise memory size will be 0.
> > +
> 
> I guess would better be folded into the other `mem=nn[KMG]' description 
> above, possibly between [ARM64] and [X86] so as to keep the order roughly 
> alphabetic.

I deliberately put hexagon separately because it stands out being the only
arch that has no other means of memory detection except mem=
 
>   Maciej

-- 
Sincerely yours,
Mike.

On Wed, 9 Mar 2022, Mike Rapoport wrote:

> >  This:
> > 
> > > +	mem=nn[KMG]	[HEXAGON] Set the memory size.
> > > +			Must be specified, otherwise memory size will be 0.
> > > +
> > 
> > I guess would better be folded into the other `mem=nn[KMG]' description 
> > above, possibly between [ARM64] and [X86] so as to keep the order roughly 
> > alphabetic.
> 
> I deliberately put hexagon separately because it stands out being the only
> arch that has no other means of memory detection except mem=

 I don't know how other people, but I'd not expect duplicate entries in 
this file and would simply miss any subsequent one(s).  Even more so if 
not adjacent such as in this case.

  Maciej