On Apr 22, 2009, at 9:26 PM, David Gibson wrote:
On Wed, Apr 22, 2009 at 04:55:42PM -0500, Kumar Gala wrote:
On Apr 22, 2009, at 4:38 PM, Scott Wood wrote:
Kumar Gala wrote:
I disagree. If you update your kernel you should update your
device
tree (thus we have .dts in the kernel tree and not somewhere else).
No. The device tree is a means to pass information from the
firmware
to the kernel. It is part of the firmware. That the repository of
trees is in the Linux kernel for any boards which are not
including the
tree inside a bootwrapper is a historical accident.
I think its a point of view argument. I don't agree its part of the
firmware, at least not part of the firmware we use (u-boot).
It's not so much point of view as situation. Putting the device tree
in the firmware and putting the device tree in the kernel are both
valid choices, with their own distinct advantages and drawbacks. With
OF it's clearly in the firmware, with cuboot it's clearly in the
kernel. With modern u-boot, it's a bit fuzzier. But if the dts is
flashed into the device in the same way as the bootloader, then it's
fair to avoid having to change it, in the same way we usually provide
workarounds to work with old firmware versions.
I think this all sounds great in theory but in reality the vast
majority (I'd say over 80-90%) we are talking about embedded reference
boards. They are subject to change as we evolve support over time.
Our firmware isn't well defined and stable like a x86 PC system or
true OF platform. I will also say we have made mistakes as learned
from them and one we keep repeating is NOT ensuring at a minimum that
all parts of the SOC memory map are actually described in the device
tree to start with.
If I look at the MPC8572 SoC from FSL I will see that the following
items aren't described today:
* Local access windows
* ECM
* GPIO - we have a binding and its possible the board doesn't use them
* PME
* TLU
* perf mon
* watchpoint debug
We also don't describe the following interrupt sources:
* ECM
* perf mon
* GPIO
* PME
* TLU
* IEEE 1588
Until we meet the most basic level of properly describing 95% of the
HW I don't see the value you guys prescribe to FW compatibility.
Additionally I believe for embedded developers its perfectly
reasonable to expect them (if they are using u-boot) to possibly have
to update their .dts/dtb if they want to update their kernel.
- k
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