Add a 128M layout for the BMC flash chip we didn't boot from. Including
this allows the user to write to each partition on the alternate spi
chip. This dtsi follows the existing standard of using the same layout
as non alt version and prepending `alt` to each partition's name.

Testing: Include this in msx4 and cat size, offsets and name
```
for devdir in /sys/class/mtd/mtd*; do
>     [[ -d $devdir && -r $devdir/name ]] || continue
>     name=$(<"$devdir/name")
>     [[ $name == alt* ]] || continue
>
>     size=$(<"$devdir/size")
>     offset=0
>     [[ -r $devdir/offset ]] && offset=$(<"$devdir/offset")
>
>     dev=$(basename "$devdir")
>     printf "%s name=%s offset=0x%X size=0x%X\n" "$dev" "$name" \
>        "$offset" "$size"
> done
mtd10 name=alt-rofs offset=0xA00000 size=0x5600000
mtd11 name=alt-rwfs offset=0x6000000 size=0x2000000
mtd7 name=alt-u-boot offset=0x0 size=0xE0000
mtd8 name=alt-u-boot-env offset=0xE0000 size=0x20000
mtd9 name=alt-kernel offset=0x100000 size=0x900000
```

Signed-off-by: Marc Olberding <molberding@nvidia.com>
---
 .../dts/aspeed/openbmc-flash-layout-128-alt.dtsi   | 32 ++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/arch/arm/boot/dts/aspeed/openbmc-flash-layout-128-alt.dtsi b/arch/arm/boot/dts/aspeed/openbmc-flash-layout-128-alt.dtsi
new file mode 100644
index 0000000000000000000000000000000000000000..08ce2eab472c3da4aa3d841adb0eb1c971e6a25a
--- /dev/null
+++ b/arch/arm/boot/dts/aspeed/openbmc-flash-layout-128-alt.dtsi
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+partitions {
+	compatible = "fixed-partitions";
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	u-boot@0 {
+		reg = <0x0 0xe0000>; // 896KB
+		label = "alt-u-boot";
+	};
+
+	u-boot-env@e0000 {
+		reg = <0xe0000 0x20000>; // 128KB
+		label = "alt-u-boot-env";
+	};
+
+	kernel@100000 {
+		reg = <0x100000 0x900000>; // 9MB
+		label = "alt-kernel";
+	};
+
+	rofs@a00000 {
+		reg = <0xa00000 0x5600000>; // 86MB
+		label = "alt-rofs";
+	};
+
+	rwfs@6000000 {
+		reg = <0x6000000 0x2000000>; // 32MB
+		label = "alt-rwfs";
+	};
+};

-- 
2.34.1

Hi Marc,

Regarding the subject prefix, can you please capitalise the 'ARM' portion, so:

   ARM: dts: aspeed: add an alt 128M flash layout

That way it's consistent with the rest of history.

On Thu, 2025-12-18 at 10:48 -0800, Marc Olberding wrote:
> Add a 128M layout for the BMC flash chip we didn't boot from. Including
> this allows the user to write to each partition on the alternate spi
> chip. This dtsi follows the existing standard of using the same layout
> as non alt version and prepending `alt` to each partition's name.
> 
> Testing: Include this in msx4 and cat size, offsets and name

I think this would be better with s/Testing/Tested by/ and associated
grammar fixes.

> ```
> for devdir in /sys/class/mtd/mtd*; do
> >     [[ -d $devdir && -r $devdir/name ]] || continue
> >     name=$(<"$devdir/name")
> >     [[ $name == alt* ]] || continue
> > 
> >     size=$(<"$devdir/size")
> >     offset=0
> >     [[ -r $devdir/offset ]] && offset=$(<"$devdir/offset")
> > 
> >     dev=$(basename "$devdir")
> >     printf "%s name=%s offset=0x%X size=0x%X\n" "$dev" "$name" \
> >        "$offset" "$size"
> > done
> mtd10 name=alt-rofs offset=0xA00000 size=0x5600000
> mtd11 name=alt-rwfs offset=0x6000000 size=0x2000000
> mtd7 name=alt-u-boot offset=0x0 size=0xE0000
> mtd8 name=alt-u-boot-env offset=0xE0000 size=0x20000
> mtd9 name=alt-kernel offset=0x100000 size=0x900000
> ```

Can you rather remove the markdown codeblock and instead indent the
code snippet (IMO 4 spaces is fine)?

Also the shell continuation markers seem a little unfortunate. Maybe
just drop them for clarity? You can separate the output from the
script.

I also found this helpful:

    diff -u arch/arm/boot/dts/aspeed/openbmc-flash-layout-128{,-alt}.dtsi

Andrew