On Tue, 25 Oct 2016 11:51:38 +0530, Madhu K said: > If in case Device tree is not there, where and how to pass the hardware > information to the linux kernel. For many types of hardware, the bus protocol provides a standard way to find everything on the bus. And that sort of bus scanning is how non-embedded systems find all their devices. If it's a laptop or a desktop or server, there's always the possibility that the user has plugged in a new graphics card or a different network card - so being able to scan and detect is important there. However, in an embedded system, the configuration is fixed - all the parts are soldered in place, and there's no place to add new devices. So the hardware designers save the US$0.08 per chip by picking stripped down chips that don't have full function (for instance, leave off the PCI config circuitry and just provide a hardwired "this device will live at this address permanently") And yes, if you're building microwave ovens, and selling 10 million of them, suddenly saving 8 cents US per chip adds up to some major profits... > Does all embedded systems contains Device tree? No, only embedded systems that have I/O devices that cannot be enumerated by the hardware. So for instance, usually a PCI device or a USB device can be detected by a bus scan. So if that's all you have, you don't need device tree - the system can find all the hardware resources. But if you have GPIO pins, or an audio or ethernet card that's hard-wired in some non-scannable way, or weird clock chips, or anything like that, you'll need device tree. And it's certainly possible to do *both* - let the kernel scan for PCI and USB devices, *and* provide a device tree for non-scannable resources.
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