Am 14.05.2014 19:30, schrieb Rob Herring:
On Wed, May 14, 2014 at 11:23 AM, Alexander Holler <hol...@ahsoftware.de> wrote:
Am 14.05.2014 18:05, schrieb Grant Likely:
On Wed, May 14, 2014 at 4:02 PM, Alexander Holler <hol...@ahsoftware.de>
wrote:
Am 14.05.2014 16:19, schrieb Grant Likely:
Rather than a dtb schema change, for the most common properties (irqs,
clocks, gpios), we could extract dependencies at boot time. I don't like
the idea of adding a separate depends-on property because it is very
easy to get it out of sync with the actual binding data (dtc is not the
only tool that manipulates .dtbs. Firmware will fiddle with it too).
Then that stuff has to fiddle correct. Sorry, but trying to solve all
problems right from the beginning just leads to endless talks with no end
and nothing will happen at all because nobody aggrees how to start.
I appreciate the problem that you're trying to solve and why you're
using the dtc approach. My job is to poke at the solution and make
sure it is going to be reliable. Making sure all users know how to
fiddle with the new property correctly is not a trivial problem,
especially when it is firmware that will not necessarily be updated.
The answer is just that they don't have to use this feature.
It's not just about users, but maintainers have to carry the code and
anything tied to DT is difficult to change or remove.
Lots of inter-dependencies are already described in DT. We should
leverage those first and then look at how to add dependencies that are
not described.
Again, that's what this feature is about. One of the problems it solves
is that those dependencies which are described in the DT source in form
of phandle reference, do disappear in the blobs because the init-system
would have to know all bindings in order to identify phandle references
(the dependencies) again.
It is more meant as a long-term solution to fix for the problem of
increasing hard-coded workarounds which all are trying to fix the
initialization order of drivers. Hardware has become a lot more complicated
than it was in the good old days, and I think the time is right trying to
adopt the init-system to this new century instead of still adding
workarounds here and there.
I don't know when the good old days were, but this has been a problem
in embedded systems for as long as I have worked on Linux.
Yes, but stuff wasn't as complicated as today, which means it was
relatively easy to manualy solve dependency problems. But if you look at
complicated SOCs like the OMAP, it's much better to let the machine
solve the dependencies to get the initialization order instead of still
trying to do this manually.
I'm not saying flat out 'no' here, but before I merge anything, I have
to be reasonably certain that the feature is not going to represent a
maintenance nightmare over the long term.
The maintenance nightmare is already present in form of all the workarounds
which are trying to fix the initialzation order necessary for modern
hardware.
Do you have concrete examples or cases where deferred probe does not work?
Why do people come back to the deferred probe stuff?
One of the biggest problem of the deferred probe stuff is the problem
how to identify real problems if everything ends up with a deferred
probe when an error occurs? That means if you display an error whenever
something is deferred, the log becomes almost unreadable. If you don't
display an error, you never will see an error. And how do you display
the real error when deferred probes finally do fail? The deferred probe
stuff doesn't has any information about the underlying error, so it
can't display it.
Anyway, this feature is totally independ of the deferred probe stuff and
both can friendly live together.
Regards,
Alexander Holler
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