[U-Boot] U-Boot Timer Qualification

[Wolfgang Denk]

Dear Ladislav Michl,

In message <20090428151147.GA19683 at linux-mips.org> you wrote:
> 
> a lot of changes are entering arm tree, many without any commit message.
> And now we have some special cases which needs some special care for yet
> unclear reason. OMAP3 timer precission was discussed to death and patch
> still didn't went in, because it needs to be verified against some
> document you are claiming is not mandatory.

Just in case there is any doubt here:

There is no, and I say *no*, mandatory verification of any timing
precision in U-Boot.

We all agree that precision is a good thing to have, it it must come
at a reasonable effort, and there is no reason to drive it into
extreme precision.

Clock signals may need an accuracy of 1 or 2% or better - as we may
see character corruption if the baudrate generators are off too far -
but this is usually a hardware issue in the first place.

System timers (like udelay() etc.) in U-Boot do not need such a level
of accuracy. That does not mean we should intentionally be inaccurate.

And of course actual testing is good, and documentation of the test
results is even better.

But: it is not mandatory. Not in U-Boot (and also not in Linux, to the
best of my knowledge).

> I'll omit more comments to this topic until my objections get answered.
> Just one side note: Both methods can be easily set in code, freeing
> every and each developer from reimplementing test case. Such code could
> be one for all and selfexplaining. Is it worth doing using current timer
> API?

See my previuous posting. I don;t think that a generic test method
that works on all boards would be possible.

Best regards,

Wolfgang Denk

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