device tree , arm and linux

linux 3.0 以後。ARM 也開始使用 Device Tree.

各platform , chip 的 device tree 寫在 arch/arm/boot/dts

build kernel 時，kernel 與 dts file 會分開 build.
dts 會用 device tree compile compile 成 DTB 檔。

bootloader 啟動 kernel 時，會同時把 DTB 讀入記憶體，交給 kernel.
kernel 啟動後，在 arch/arm/kernel/setup.c : setup_arch( ) 中

unflatten_device_tree();

負責把 DTB 解成 device tree 結構。

driver/of/fdt.c:

/**
 * unflatten_device_tree - create tree of device_nodes from flat blob
 *
 * unflattens the device-tree passed by the firmware, creating the
 * tree of struct device_node. It also fills the "name" and "type"
 * pointers of the nodes so the normal device-tree walking functions
 * can be used.
 */
void __init unflatten_device_tree(void)
{
 __unflatten_device_tree(initial_boot_params, &of_allnodes,
    early_init_dt_alloc_memory_arch);

 /* Get pointer to "/chosen" and "/aliasas" nodes for use everywhere */
 of_alias_scan(early_init_dt_alloc_memory_arch);
}

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ref:

• http://events.linuxfoundation.org/sites/events/files/slides/petazzoni-device-tree-dummies.pdf
• http://blog.csdn.net/21cnbao/article/details/8457546
• https://sites.google.com/site/yucheng1102/linux-kernel/device-tree
• http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=dfcd04b19d16c0016c705ed96a8b3cfa5315a2e9