[PATCH 2/2] [POWERPC] Describe memory-mapped RAM&ROM chips of bindings

[PATCH 2/2] [POWERPC] Describe memory-mapped RAM&ROM chips of bindings

[Laurent Pinchart]

Signed-off-by: Laurent Pinchart <laurentp@cse-semaphore.com>
=2D--
 Documentation/powerpc/booting-without-of.txt |   31 ++++++++++++++++++++++=
+++-
 1 files changed, 30 insertions(+), 1 deletions(-)

diff --git a/Documentation/powerpc/booting-without-of.txt b/Documentation/p=
owerpc/booting-without-of.txt
index 7b4e8a7..53d1cf8 100644
=2D-- a/Documentation/powerpc/booting-without-of.txt
+++ b/Documentation/powerpc/booting-without-of.txt
@@ -57,7 +57,8 @@ Table of Contents
       n) 4xx/Axon EMAC ethernet nodes
       o) Xilinx IP cores
       p) Freescale Synchronous Serial Interface
=2D	  q) USB EHCI controllers
+      q) USB EHCI controllers
+      r) Memory-mapped RAM & ROM
=20
   VII - Specifying interrupt information for devices
     1) interrupts property
@@ -2816,6 +2817,34 @@ platforms are moved over to use the flattened-device=
=2Dtree model.
 		   big-endian;
 	   };
=20
+   r) Memory-mapped RAM & ROM
+
+    Dedicated RAM and ROM chips are often used as storage for temporary or
+    permanent data in embedded devices. Possible usage include non-volatile
+    storage in battery-backed SRAM, semi-permanent storage in dedicated SR=
AM
+    to preserve data accross reboots and firmware storage in dedicated ROM.
+
+     - compatible : should contain the specific model of RAM/ROM chip(s)
+       used, if known, followed by either "physmap-ram" or "physmap-rom"
+     - reg : Address range of the RAM/ROM chip
+     - bank-width : Width (in bytes) of the RAM/ROM bank. Equal to the
+       device width times the number of interleaved chips.
+     - device-width : (optional) Width of a single RAM/ROM chip. If
+       omitted, assumed to be equal to 'bank-width'.
+
+    Similarly to memory-mapped NOR flash, memory-mapped RAM & ROM chips
+    can be partionned. See the "j) CFI and JEDEC memory-mapped NOR flash"
+    section for information about how to represent partitions in the
+    device tree.
+
+    Example:
+
+	mmram@f2000000 {
+		compatible =3D "renesas,m5m5w816", "physmap-ram";
+		reg =3D <f2000000 00100000>;
+		bank-width =3D <2>;
+	};
+
=20
    More devices will be defined as this spec matures.
=20
=2D-=20
1.5.0


=2D-=20
Laurent Pinchart
CSE Semaphore Belgium

Chauss=E9e de Bruxelles, 732A
B-1410 Waterloo
Belgium

T +32 (2) 387 42 59
=46 +32 (2) 387 42 75

Re: [PATCH 2/2] [POWERPC] Describe memory-mapped RAM&ROM chips of bindings

[Segher Boessenkool]

> +    Dedicated RAM and ROM chips are often used as storage for 
> temporary or
> +    permanent data in embedded devices. Possible usage include 
> non-volatile
> +    storage in battery-backed SRAM, semi-permanent storage in 
> dedicated SRAM
> +    to preserve data accross reboots and firmware storage in 
> dedicated ROM.
> +
> +     - compatible : should contain the specific model of RAM/ROM 
> chip(s)
> +       used, if known, followed by either "physmap-ram" or 
> "physmap-rom"
> +     - reg : Address range of the RAM/ROM chip
> +     - bank-width : Width (in bytes) of the RAM/ROM bank. Equal to the
> +       device width times the number of interleaved chips.
> +     - device-width : (optional) Width of a single RAM/ROM chip. If
> +       omitted, assumed to be equal to 'bank-width'.

Maybe I'm rehashing some old discussion here, if so, sorry; but why
do you have bank-width and device-width here?  What useful information
does it provide?  If this is about saying what the preferred (or only
possible) access width is, better names are in order.


Segher

Re: [PATCH 2/2] [POWERPC] Describe memory-mapped RAM&ROM chips of bindings

[Laurent Pinchart]

On Wednesday 26 March 2008 15:52, Segher Boessenkool wrote:
> > +    Dedicated RAM and ROM chips are often used as storage for=20
> > temporary or
> > +    permanent data in embedded devices. Possible usage include=20
> > non-volatile
> > +    storage in battery-backed SRAM, semi-permanent storage in=20
> > dedicated SRAM
> > +    to preserve data accross reboots and firmware storage in=20
> > dedicated ROM.
> > +
> > +     - compatible : should contain the specific model of RAM/ROM=20
> > chip(s)
> > +       used, if known, followed by either "physmap-ram" or=20
> > "physmap-rom"
> > +     - reg : Address range of the RAM/ROM chip
> > +     - bank-width : Width (in bytes) of the RAM/ROM bank. Equal to the
> > +       device width times the number of interleaved chips.
> > +     - device-width : (optional) Width of a single RAM/ROM chip. If
> > +       omitted, assumed to be equal to 'bank-width'.
>=20
> Maybe I'm rehashing some old discussion here, if so, sorry; but why
> do you have bank-width and device-width here?  What useful information
> does it provide?  If this is about saying what the preferred (or only
> possible) access width is, better names are in order.

device-width isn't used so we can get rid of it. bank-width is used by the=
=20
map_ram driver for erase operations (mapram_erase in=20
drivers/mtd/chips/map_ram.c). To be honest I'm not sure why it uses such an=
=20
inefficient approach instead of memsetting the whole area.

=2D-=20
Laurent Pinchart
CSE Semaphore Belgium

Chauss=E9e de Bruxelles, 732A
B-1410 Waterloo
Belgium

T +32 (2) 387 42 59
=46 +32 (2) 387 42 75

Re: [PATCH 2/2] [POWERPC] Describe memory-mapped RAM&ROM chips of bindings

[David Gibson]

On Thu, Mar 27, 2008 at 10:37:17AM +0100, Laurent Pinchart wrote:
> On Wednesday 26 March 2008 15:52, Segher Boessenkool wrote:
> > > +    Dedicated RAM and ROM chips are often used as storage for 
> > > temporary or
> > > +    permanent data in embedded devices. Possible usage include 
> > > non-volatile
> > > +    storage in battery-backed SRAM, semi-permanent storage in 
> > > dedicated SRAM
> > > +    to preserve data accross reboots and firmware storage in 
> > > dedicated ROM.
> > > +
> > > +     - compatible : should contain the specific model of RAM/ROM 
> > > chip(s)
> > > +       used, if known, followed by either "physmap-ram" or 
> > > "physmap-rom"
> > > +     - reg : Address range of the RAM/ROM chip
> > > +     - bank-width : Width (in bytes) of the RAM/ROM bank. Equal to the
> > > +       device width times the number of interleaved chips.
> > > +     - device-width : (optional) Width of a single RAM/ROM chip. If
> > > +       omitted, assumed to be equal to 'bank-width'.
> > 
> > Maybe I'm rehashing some old discussion here, if so, sorry; but why
> > do you have bank-width and device-width here?  What useful information
> > does it provide?  If this is about saying what the preferred (or only
> > possible) access width is, better names are in order.
> 
> device-width isn't used so we can get rid of it. bank-width is used by the 
> map_ram driver for erase operations (mapram_erase in 
> drivers/mtd/chips/map_ram.c). To be honest I'm not sure why it uses such an 
> inefficient approach instead of memsetting the whole area.

Sounds like bank-width is meaningless then, and doesn't belong in the
device tree.  The shim which instantiates the mtd device from the
device tree can make something up.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson