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-rw-r--r--Documentation/superio/common/ssdt.md56
-rw-r--r--Documentation/superio/index.md3
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diff --git a/Documentation/superio/common/ssdt.md b/Documentation/superio/common/ssdt.md
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@@ -0,0 +1,56 @@
+# SuperIO SSTD generator
+
+This page describes the common SSDT ACPI generator for SuperIO chips that can
+be found in coreboot.
+
+## Functional description
+
+In order to automatically generate ACPI functions you need to add
+a new `chip superio/common` and `device pnp xx.0 on` to your devicetree.
+
+The xx denotes the hexadecimal address of the SuperIO.
+
+Place the regular LDN pnp devices behind those two entries.
+
+The code will automatically guess the function based on the decoded
+I/O range and ISA IRQ number.
+
+## Example devicetree.cb
+
+This example is based on AST2400.
+
+```code
+# Add a "container" for proper ACPI code generation
+chip superio/common
+ device pnp 2e.0 on # just for the base device, not for the LDNs
+ chip superio/aspeed/ast2400
+ device pnp 2e.0 off end
+ device pnp 2e.2 on # SUART1
+ io 0x60 = 0x3f8
+ irq 0x70 = 4
+ end
+ device pnp 2e.3 on # SUART2
+ io 0x60 = 0x2f8
+ irq 0x70 = 3
+ end
+ device pnp 2e.4 on # SWC
+ io 0x60 = 0xa00
+ io 0x62 = 0xa10
+ io 0x64 = 0xa20
+ io 0x66 = 0xa30
+ irq 0x70 = 0
+ end
+ end
+ end
+end
+```
+
+## TODO
+
+1) Add ACPI HIDs to every SuperIO driver
+2) Don't guess ACPI HID of LDNs if it's known
+3) Add "enter config" and "exit config" bytes
+4) Generate support methods that allow
+ * Setting resource settings at runtime
+ * Getting resource settings at runtime
+ * Disabling LDNs at runtime
diff --git a/Documentation/superio/index.md b/Documentation/superio/index.md
index eef4d579ef..39965fde07 100644
--- a/Documentation/superio/index.md
+++ b/Documentation/superio/index.md
@@ -5,3 +5,6 @@ This section contains documentation about coreboot on specific SuperIOs.
## Nuvoton
- [NPCD378](nuvoton/npcd378.md)
+
+## Common
+- [SSDT generator for generic SuperIOs](common/ssdt.md)