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

[tglx@linutronix.de (Thomas Gleixner)]

On Thu, 21 Apr 2011, Mark Brown wrote:
> 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 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.
> 
> There's nothing intrinsic about the concept of a clock which means that
> it needs to be memory mapped or have a particular set of registers for
> us to work with.  This sounds like something that ought to be factored
> out but it's not obvious to me that it should be part of the core struct.

Care to look over the various implementations and find out that a lot
of them look like:

static int _clk_enable(struct clk *clk)
{
        unsigned int reg;

        reg = __raw_readl(clk->enable_reg);
        reg |= 1 << clk->enable_shift;
        __raw_writel(reg, clk->enable_reg);

        return 0;
}

Just in about 100 variations of the theme. Which is basically the same
as we have in irq chip implementations. And I showed how much of these
things can be factored out when done right. And even if a particular
clock does not implement enable/disable calls, then having
regs.enable_reg around is not a problem.

That's not a requirement for the first step, but I want to see people
thinking about it instead of mindlessly converting their clocks to the
generic clock structure and the generic handling functions. And I'd
rather see people coming and say: We see that the following thing
would be cute:

      clk_regs {
      	       struct spin_lock *reg_lock;
      	       void *base;
	       union {
	       	       void *enable_reg;
	       	       unsigned long enable_offset;
	       };
	       ....
	       u32 enable_cache;
      };

Because that's what we implement via container_of now. And we can add
such stuff which is obvious right away.

Thanks,

	tglx