[PATCH v4 1/2] ARM: keystone: pm: switch to use generic pm domains

Grygorii Strashko grygorii.strashko at ti.com
Tue Nov 25 03:08:57 PST 2014

Hi Arnd,

On 11/25/2014 12:33 PM, Arnd Bergmann wrote:
> On Monday 24 November 2014 22:44:06 Mike Turquette wrote:
>> Quoting Arnd Bergmann (2014-11-24 02:50:28)
>>> Could the driver maybe identify the clocks that it wants to manage itself
>>> to the pm-domain code? If it's safe for a device to have the clock turned
>>> on at the default rate before loading the driver, any device that is connected
>>> to the simple clk-pm-domain code could have all its clocks start out as
>>> owned by the pm-domain, but then claim the clocks it needs to reprogram for
>>> itself and take them out of the pmdomain.
>> I was thinking along similar lines. The functional versus optional stuff
>> is really a property of the consuming device, not the clock signal
>> itself.
>> Instead of adding a new property to the clock binding (e.g. fck-clocks
>> or optional-clocks), could we simply wrap those lists of clocks in
>> another node? E.g:
>> mandatory-clocks {
>>         clocks = <&papllclk>, <&clkcpgmac>;
>>         clock-names = "clk_pa", "clk_cpgmac";
>> }
>> clocks = <&papllclk>, <&clkcpgmac>, <&chipclk12>;

optional-clocks { ?
>>         clocks = <&clkcpgmac>;         

	   clocks = <&chipclk12>; ?

>>         clock-names = "cpsw_cpts_rft_clk";
>> }
>> I'm showing my DT ignorance on this one. I haven't really thought
>> through how these sub-nodes would work with of_clk_* handlers in
>> drivers/clk/clkdev.c.

As I remember, there was nack for sub-nodes approach from Olof :(
"[RFC 0/2] pwrseq: Add subsystem for power sequences"

> I'm not sure I even understand what you intended the example to look
> like, it does't parse ;-)
> My point above was completely different, the suggestion I made was
> to not classify the clocks in DT at all, but to leave it all in
> the client driver.

I slept with this idea :) From one side it sounds good. Pls, Correct me if I'm wrong:
- there still will be "simple-pmdomain" and all devices will be attached to it by
   default (or as specified in DT power-domains = <&simple_pmdomain>;);
- drivers will use smth. like pm_clk_remove() to remove optional clocks from pm_clk;

>From another side:
- drivers will get dependency from pm_clk;
- HW limitations can't be taken into account - it's possible that some clocks should
  not be enabled until it's allowed. And only driver know when it's allowed.
  Otherwise, HW state may become unspecified or wrong output can be generated.


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