[U-Boot] core ticks/timer code

[Wolfgang Denk]

Dear Mike Frysinger,

In message <200903310513.09082.vapier at gentoo.org> you wrote:
>
...
> > I've in mind to partially import the clocksource linux API or create a new
> > U-Boot api devired from it's design
>
> the clocksource framework in linux sounds like extreme overkill for u-boot.
> where do you see realistic usage of more than one timer ?  u-boot is pretty
> much a single threaded app that polls.

Correct. We definitely do not need the full capabilities of the Linux
framework. Any new implementation will be checked against the current
code, and memory foot print is something we will check carefully.

OTOH, I think Sascha's u-boot-v2 uses code that was derived from the
Linux code, but in a pretty lean way. It may be interesting to check
there...

> > I'll propose a new design with the following Requierement
> >
> > Generic delay function implementation
> >  - ndelay()
> >  - udelay()
> >  - mdelay()
> >
> > Generic helper
> >  - khz2cycles()
> >  - hz2cycles()
> >  - cs2ns()
> >
> > Timer API
> >  - timer_init()		- setup the timer
> >  - timer_reset()	- reset the timer (use in case of overflow)
> >  - get_ticks()		- return the current ticks
> >  - get_cycles()		- return the ticks frequency in ns
>
> do you have real use cases here ?  i'd actually propose the opposite: kill off 
> the notion of "ticks", "cycles", and "hz".  i dont think ndelay() is really 
> necessary, and mdelay() is a simple macro on top of udelay().  that leaves us 
> with really only the three functions we have today: timer_init(), get_timer(), 
> and reset_timer().  we clarify that the function operates in terms of 
> milliseconds and blam, it's all so simple now.

Agreed (except that we probably  cannot  completely  throw  away  the
tick;  IIRC  there  are  cases  in early startup when nothing else is
available yet).

Best regards,

Wolfgang Denk

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