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

[Vince Hsu]

On 07/21/2014 05:02 PM, Thierry Reding wrote:
> * PGP Signed by an unknown key
>
> On Mon, Jul 21, 2014 at 03:09:29PM +0800, Vince Hsu wrote:
>> On 07/17/2014 07:01 PM, Thierry Reding wrote:
>>>> Old 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?
As we talked offline yesterday, that's in 5.6.6.7 - 5.6.6.9.

Thanks,
Vince