Changes between Initial Version and Version 1 of FlattenedDeviceTree

Timestamp:

Oct 27, 2009, 5:21:43 PM (15 years ago)

Author:

Nicolas Pouillon

Comment:

--

FlattenedDeviceTree

@@ +1 @@
+Around revision [900], MutekH got support for Flattened device trees.
+
+= Rationale =
+
+Flattened device trees (FDT) are useful to get a list of all available hardware where no hardware-based enumeration exists (aka PnP, like PCI, USB, ... provides).
+
+FDT provides normalized representation of the hardware platform without adding specific initialization code.
+
+The normalization comes from IEEE1275 (aka Open Firmware); while Open Firmware also defined heavy things (like a Forth interpreter), we only use the FDT information.
+
+Using FDT is mainstream, andis also used by Linux  and BSD, supported is U-Boot and other bootloaders.
+
+= Implementation =
+
+In MutekH, FDT is handled through an hardware enumerator device driver, it behaves like the other enumerators (PCI, ISAPnP).
+
+Drivers may export themselves as FDT-aware, and define which device name string to match. For instance, the following subtree defines a tty device:
+
+{{{
+        tty@0 {
+            device_type = "soclib:tty";
+                tty_count = <1>;
+                reg = <0x90600000 0x10>;
+                icudev = &{/icu@0};
+                irq = <1>;
+        };
+}}}
+
+In turn, the SoCLib tty driver declares itself (in source:trunk/mutekh/drivers/device/char/tty-soclib/tty-soclib.c#L146) as:
+
+{{{
+static const struct devenum_ident_s     tty_soclib_ids[] =
+{
+        DEVENUM_FDTNAME_ENTRY("soclib:tty", 0, 0),
+        { 0 }
+};
+
+const struct driver_s   tty_soclib_drv =
+{
+  .class                = device_class_char,
+  .id_table             = tty_soclib_ids,
+  .f_init               = tty_soclib_init,
+  .f_cleanup            = tty_soclib_cleanup,
+  .f_irq                = tty_soclib_irq,
+  .f.chr = {
+    .f_request          = tty_soclib_request,
+  }
+};
+}}}
+
+This will make the FDT enumerator use the correct driver, matching `"soclib:tty"`