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x86 discoverability is over rated
Posted Aug 28, 2011 3:33 UTC (Sun) by giraffedata (subscriber, #1954)
I'd rather have a simple bootloader and device tree than an ACPI or EFI BIOS in my PC. Perhaps the BIOS could be chain loaded for OSes that need it.
Where would your device tree come from? I presume you could install a new graphics controller in your PC; how would the device tree get changed so Linux and the things running under it know to drive it differently than the old one?
Posted Aug 28, 2011 9:12 UTC (Sun) by nhippi (subscriber, #34640)
Device tree/DMI are more useful in telling kernel about devices that cannot be automatically scanned. Usually such devices are "soldered on", so the need of changing the Device tree is quite rare.
Life in X86 and DMI is a bit more complicated, as Bios also probes some devices and puts them in DMI. Often instead of probing those devices in kernel again, we trust the bios with varying degrees of success.
Posted Aug 28, 2011 19:18 UTC (Sun) by giraffedata (subscriber, #1954)
(There was an article about this in LWN not long ago, but I didn't get it then either).
Posted Aug 28, 2011 20:35 UTC (Sun) by robbe (subscriber, #16131)
Seems like on this device-tree system some device is not ending up under /sys/devices, or too little actual info is put there, although the kernel had it handed to it via the device tree.
Posted Aug 28, 2011 22:11 UTC (Sun) by mjg59 (subscriber, #23239)
Posted Aug 28, 2011 23:04 UTC (Sun) by giraffedata (subscriber, #1954)
Posted Aug 28, 2011 23:57 UTC (Sun) by dlang (✭ supporter ✭, #313)
on many embedded systems (including ARM) this isn't the case. the kernel running on the system has no way of guessing what will happen if it sends data out to some I/O address. The kernel must be told about every device in the system and where it is.
it's the fact that almost every device on an x86 system is on a bus that can report what is there that makes the systems "discoverable"
Posted Aug 29, 2011 0:28 UTC (Mon) by mjg59 (subscriber, #23239)
Posted Aug 29, 2011 1:39 UTC (Mon) by dlang (✭ supporter ✭, #313)
Device Trees are a way for the System Administrator who installs an OS on the system what hardware exists.
It's far more likely that the hardware manufacturer is going to accurately identify what hardware exists than it is that the System Administrator is going to know what hardware exists on a system.
Device Trees may look like they are discoverable if you are only looking at it from the point of view of an OS that has the Device Tree provided to it. But from the point of view of the person trying to install the system who has to figure out what to put in the Device Tree, they are not discoverable, they are the output of research, not the source of information.
Posted Aug 29, 2011 2:15 UTC (Mon) by mjg59 (subscriber, #23239)
Posted Aug 29, 2011 2:26 UTC (Mon) by dlang (✭ supporter ✭, #313)
ARM vendors don't really care about Device Trees, they are pretty happy just hard-coding the kernel itself.
it's the people who want to upgrade the devices and people who want to maintain the upstream tree that want the consolidation made available by device trees.
Posted Oct 18, 2011 16:15 UTC (Tue) by jcm (subscriber, #18262)
Posted Aug 29, 2011 0:32 UTC (Mon) by mjg59 (subscriber, #23239)
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