Am 14.05.2014 21:06, schrieb Rob Herring:
On Wed, May 14, 2014 at 12:45 PM, Alexander Holler <holler@xxxxxxxxxxxxx> wrote:
Am 14.05.2014 19:30, schrieb Rob Herring:
On Wed, May 14, 2014 at 11:23 AM, Alexander Holler <holler@xxxxxxxxxxxxx>
wrote:
Am 14.05.2014 18:05, schrieb Grant Likely:
On Wed, May 14, 2014 at 4:02 PM, Alexander Holler <holler@xxxxxxxxxxxxx>
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.
They don't disappear, but they become binding specific to recover.
What you are loosing is type information which is something we would
like to solve as well.
You can regenerate or figure out the dependencies with knowledge of
the binding. The of_irq_init code does this. Maintaining this
information in the dtb that can be parsed in a generic way and having
the kernel handle non-bus oriented dependencies are really 2 separate
problems. Let's not try to solve it all at once.
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?
Because it is there today and generally works.
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.
This all sounds like "I don't like deferred probe because it is hard
to debug" to me. This all sounds solvable with better instrumentation
and debug capability. Why probe is deferred should be available at the
source when deciding to return -EPROBE_DEFER.
I still have not seen an example of A depends on B, deferred probe
fails because of ? and here is the code for A that works around the
problem.
Anyway, this feature is totally independ of the deferred probe stuff and
both can friendly live together.
Yes, except then we get to maintain both.
Goodbye and thanks for all the fish.
Sorry, but my patience in dealing with Linux kernel maintainers was
already almost zero before I've posted these patches and I have to
realize that only fools still try to do so.
Alexander Holler
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