[U-Boot] [PATCH 3/8] boottime: Add core boottime measurement support

[Lee Jones]

> > Yes, I intend to extend this functionality into Device Tree.
> > That way it will be architecture and OS independent.
> > 
> > > And forcing something upon a mechanism that was designed for a
> > > completely different purpose, where you see right from the first
> > > glance that it does  not math easily?
> > 
> > Not entirely sure what you mean here. This mechanism works
> > perfectly with ATAGs.
> 
> Neither ATAGS not the device tree are intended nor designed for
> passing logfile information.  Yes, you can use them like that, and it
> will actually work.

ATAGs were exactly designed for this type of thing. To pass small
data structures though to the kernel. In our case, our trace-points
are held in a small data structure. They're not logs.
 
> You can also drive a nail in using a microscope as hammer.

Ah good idea. I have to try this. ;)

> > > The advantages should be obvious: we will need no extra kernel
> > > modification, we do not depend on ATAGS, and we are automatically
> > > architecture-independent.
> > 
> > Wouldn't this clog up the kernel's log buffer? I'm sure no
> > user wants to see reams of otherwise useless logging scrawled
> > throughout their bootlog. We'd also have a write a text parser
> > to obtain the information for processing. It would be easier
> > to either pass in a struct, as we do with the ATAG mechanism,
> > or though Device Tree as previously discussed.
> 
> I think these are pretty poor arguments.  There are standard methods
> (like log levels) to provide adequate filtering of which messages are
> passed on to a user.  An there exists a plethora of tools for
> automatic filtering and post-processing of syslog messages.  You will
> need to write _less_ code than with your homebrew implementation.

They're not poor augments if the data stored isn't log messages,
which these aren't. If anything I would say that ramming them in as
textual kernel messages, then parsing the log text using a userspace
tool was an abuse of the system. If we create them as data in the
bootloader, then pass them to the kernel as data, then process them
as data, _that_ would be the correct mechanism.

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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