From mboxrd@z Thu Jan 1 00:00:00 1970 From: madhu.sk89@gmail.com (Madhu K) Date: Tue, 25 Oct 2016 15:46:05 +0530 Subject: Device Tree In-Reply-To: <32232.1477381176@turing-police.cc.vt.edu> References: <32232.1477381176@turing-police.cc.vt.edu> Message-ID: To: kernelnewbies@lists.kernelnewbies.org List-Id: kernelnewbies.lists.kernelnewbies.org 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, 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. > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20161025/b41b9786/attachment.html