Device Tree

[Madhu K]

Hi Valdis,

You mean In non embedded system( laptop, desktop and server ) DT is not at
all required?

Regards,
Madhu

On Tue, Oct 25, 2016 at 1:09 PM, <Valdis.Kletnieks at vt.edu> wrote:

> 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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