Re: [PATCH 12/12] ARM: tegra: Convert PMC to a driver

[Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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On Mon, Jul 21, 2014 at 03:09:29PM +0800, Vince Hsu wrote:
> 
> On 07/17/2014 07:01 PM, Thierry Reding wrote:
> >* PGP Signed by an unknown key
> >
> >On Thu, Jul 17, 2014 at 12:01:56PM +0300, Peter De Schrijver wrote:
> >>On Thu, Jul 17, 2014 at 10:53:08AM +0200, Peter De Schrijver wrote:
> >>>On Wed, Jul 16, 2014 at 08:57:16PM +0200, Thierry Reding wrote:
> >>>>>Old Signed by an unknown key
> >>>>On Wed, Jul 16, 2014 at 05:22:03PM +0200, Arnd Bergmann wrote:
> >>>>>On Wednesday 16 July 2014 17:14:29 Thierry Reding wrote:
> >>>>>>>Ok, I'll have a look. I think when this becomes a separate driver, it
> >>>>>>>should also have its own header file, so maybe you can in the meantime
> >>>>>>>make it a local header file in mach-tegra until we have found a good
> >>>>>>>place for it.
> >>>>>>Why do you think it should be a separate header? We already have a
> >>>>>>couple in include/linux and I'm not sure it's useful to add even more.
> >>>>>>If anything I would've thought it made sense to move the content of the
> >>>>>>other headers into tegra-soc.h.
> >>>>>I very much dislike the idea of having a per-vendor header file that
> >>>>>everything gets crammed into. We should try to have proper subsystems
> >>>>>and generic interfaces for these wherever possible.
> >>>>I completely agree. However spreading the SoC-specific functions across
> >>>>multiple header files isn't going to help. If we keep all the per-vendor
> >>>>APIs in one file it makes it easier to see what could still be moved off
> >>>>into a separate subsystem.
> >>>>
> >>>>Now for PMC specifically, we've investigated converting the powergate
> >>>>API to power domains. I don't think it will be possible to make that
> >>>>work. The issue is that there's a defined sequence that needs to be
> >>>>respected to make sure the device is powered up properly. That sequence
> >>>>involves the primary clock and reset of the device. It's been proposed
> >>>>to make these clocks available to the PMC driver so that it can control
> >>>>them, but then we can't make sure that clocks are really off if they
> >>>>need to be, since we have two drivers accessing them. The only way I see
> >>>resets do not have reference counts, so they can be controlled by a
> >>>powerdomain driver without any problems. For clocks, there would only be
> >>>a problem for the module clocks if the drivers don't use runtime PM. If
> >>>we move all drivers to runtime PM, the clock control can move into the
> >>>powerdomain code and runtime PM will ensure domains are not turned off
> >>>with active modules.
> >>>
> >>>>to make that work reliably is by moving complete control of the
> >>>>powergate into drivers so that they can make sure clocks and resets are
> >>>>in the correct states.
> >>>>
> >>>Which won't work if you have domains which contain several modules.
> >>We also need to control the memory clients in the domains using
> >>MC_CLIENT_HOTRESET_CTRL.
> >Oh, great. More interdependencies...
> Some domains depend on others. Can we take this into account?

I'm not aware of any dependencies. Can you point me at the relevant
section in the TRM?

Thierry

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