[U-Boot] core ticks/timer code

[Jean-Christophe PLAGNIOL-VILLARD]

On 12:28 Tue 31 Mar     , Wolfgang Denk wrote:
> 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.
That's why I've tell to partially import it as have done Sascha in u-boot V2
> 
> 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've take a look on it and it's the idea I've in mind to do also
> 
> > > 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.
Yes I've real case where I do need ndelay to generate high speed clock with a
gpio and udelay is too slow.

we need get_cycles and get_ticks to calculate the udelay, mdelay and ndelay
otherwise how can you known the ticks frequency?
> 
> Agreed (except that we probably  cannot  completely  throw  away  the
> tick;  IIRC  there  are  cases  in early startup when nothing else is
> available yet).
not necessarely you can activate the timer just after the cpu_init
so normally you do not need any get_ticks.

Best Regards,
J.