[PATCHv4 11/15] clk: ti: clockdomain: add clock provider support to clockdomains

[Michael Turquette]

Quoting Tony Lindgren (2016-10-28 16:54:48)
> * Stephen Boyd <sboyd at codeaurora.org> [161028 16:37]:
> > On 10/28, Tony Lindgren wrote:
> > > * Tero Kristo <t-kristo at ti.com> [161028 00:43]:
> > > > On 28/10/16 03:50, Stephen Boyd wrote:
> > > > > I suppose a PRCM is
> > > > > like an MFD that has clocks and resets under it? On other
> > > > > platforms we've combined that all into one node and just had
> > > > > #clock-cells and #reset-cells in that node. Is there any reason
> > > > > we can't do that here?
> > > > 
> > > > For OMAPs, there are typically multiple instances of the PRCM around; OMAP4
> > > > for example has:
> > > > 
> > > > cm1 @ 0x4a004000 (clocks + clockdomains)
> > > > cm2 @ 0x4a008000 (clocks + clockdomains)
> > > > prm @ 0x4a306000 (few clocks + resets + power state handling)
> > > > scrm @ 0x4a30a000 (few external clocks + plenty of misc stuff)
> > > > 
> > > > These instances are also under different power/voltage domains which means
> > > > their PM behavior is different.
> > > > 
> > > > The idea behind having a clockdomain as a provider was mostly to have the
> > > > topology visible : prcm-instance -> clockdomain -> clocks
> > > 
> > > Yeah that's needed to get the interconnect hierarchy right for
> > > genpd :)
> > > 
> > > > ... but basically I think it would be possible to drop the clockdomain
> > > > representation and just mark the prcm-instance as a clock provider. Tony,
> > > > any thoughts on that?
> > > 
> > > No let's not drop the clockdomains as those will be needed when we
> > > move things into proper hierarchy within the interconnect instances.
> > > This will then help with getting things right with genpd.
> > > 
> > > In the long run we just want to specify clockdomain and the offset of
> > > the clock instance within the clockdomain in the dts files.
> > > 
> > 
> > Sorry, I have very little idea how OMAP hardware works. Do you
> > mean that you will have different nodes for each clockdomain so
> > that genpd can map 1:1 to the node in dts? But in hardware
> > there's a prcm that allows us to control many clock domains
> > through register read/writes? How is the interconnect involved?
> 
> There are multiple clockdomains, at least one for each interconnect
> instance. Once a clockdomain is idle, the related interconnect can
> idle too. So yeah genpd pretty much maps 1:1 with the clockdomains.
> 
> There's more info in for example omap4 TRM section "3.4.1 Device
> Power-Management Layout" that shows the voltage/power/clock domains.
> The interconnect instances are mostly named there too looking at
> the L4/L3 naming.

I'm confused on two points:

1) why are the clkdm's acting as clock providers? I've always hated the
name "clock domain" since those bits are for managing module state, not
clock state. The PRM, CM1 and CM2 provide the clocks, not the
clockdomains.

2) why aren't the clock domains modeled as genpds with their associated
devices attached to them? Note that it is possible to "nest" genpd
objects. This would also allow for the "Clockdomain Dependency"
relationships to be properly modeled (see section 3.1.1.1.7 Clock Domain
Dependency in the OMAP4 TRM).

Regards,
Mike

> 
> Regards,
> 
> Tony