[PATCH RFC] clk: add support for automatic parent handling

[s.hauer@pengutronix.de (Sascha Hauer)]

On Thu, Apr 21, 2011 at 11:21:53AM +0200, Thomas Gleixner wrote:
> On Thu, 21 Apr 2011, Sascha Hauer wrote:
> > On Wed, Apr 20, 2011 at 09:52:15PM +0200, Thomas Gleixner wrote:
> > >    - a field for the parent
> > >    - a field for the current clock rate
> > 
> > Currently there is no possibility to bring the clock tree in sync with
> > the hardware. clocks are not registered at all, they are just there. So
> > there is no instance who could iterate over the tree in order to bring
> > it in sync. Unless we create that (which I would like) there is no point
> > in adding rate and parent fields.
> 
> And that's where the problem starts. What's the point of that current
> conglomorate of function pointers and half baken helper wrappers if we
> don't have answers for how to populate the clk tree, how to simplify
> stuff w/o the need of tons of callbacks which have to be implemented
> all over the place ?
> 
> > Hm, thinking about this maybe we could add a CLK_IN_SYNC field which
> > is initially cleared and gets set once the get_parent()/get_rate()
> > callback has been called for a clock.
> > 
> > >    - a field for the base register
> > >    - a struct for the offsets of the most common registers relative to
> > >      base
> > 
> > What's wrong with embedding struct clk into a more specific clock and
> > access it with container_of()? It must be done anyway once a field is
> > missing in struct clk, or we end up with a lot of fields in struct clk
> > which are used in only few types of clocks.
> 
> As I explained already, that's the whole purpose of frameworks. See
> clockevents, clocksource, genirq. Lots of stuff is only used by a very
> small subset, but it's better to have that in common code than growing
> warts at all ends.
> 
> > > 
> > > The least thing which we need now are half baken "abstractions" which
> > > just shuffle code around for no value.
> > 
> > While I agree with several things you say even the half baken
> > abstractions help to bring the problems into the light. What we have now
> > is that all these problems are hidden in SoC specific abstractions which
> > all have their own problems and bugs.
> 
> And sadly enough the proposed solution keeps 90% of that crap where it
> is. So it's not a real improvement, just shuffling code around.

That's why I tried to sort out some common patterns (divider, gates,
muxes) and put them into drivers/clk for other people to use it. It's
enough to build a whole clock tree out of it (except plls and special
stuff). All things you mentioned which are missing in the common clock
stuff can be added without touching the i.MX specific parts. You want
the framework (once it actually is one) to handle the parents? just move
the parent handling out of drivers/clk/clk-[divider|mux|gate].c to
drivers/clk/clk.c. Refcounting shall be fixed? do so in
drivers/clk/clkdev.c.

I didn't say that the patches I posted shall be moved upstream as-is. I
only wanted to show how a clock tree can look like when we sort out
common patterns.

Sascha


-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |