[PATCH v5 12/44] clk: davinci: Add platform information for TI DA850 PSC

[David Lechner]

On 04/24/2018 03:28 AM, Sekhar Nori wrote:
> On Monday 23 April 2018 08:29 PM, David Lechner wrote:
>> On 04/06/2018 11:46 AM, Stephen Boyd wrote:
>>> Quoting Sekhar Nori (2018-04-06 02:37:03)
>>>>
>>>> Can you please check that and confirm there is no issue with genpd and
>>>> using CLK_OF_DECLARE() to initialize clocks?
>>>>
>>>> Unless you report an issue back, or Mike and Stephen have ideas about
>>>> how to handle the dependency between PSC/PLL derived timer clock
>>>> initialization and and timer_probe(), I think we need to move back to
>>>> using CLK_OF_DECLARE().
>>>
>>> In such a case, please use the hybrid approach where the clks required
>>> for the clockevent and/or clocksource are registered in the early
>>> CLK_OF_DECLARE path but the rest of the clks get registered with a
>>> proper platform device and driver. There are examples of this approach
>>> on other platforms already.
>>>
>>
>> I looked at this a bit last week, but I didn't come up with any approach
>> that I was happy with. It seems like it would be nice to just register
>> the absolute minimum clocks needed. On DA8XX, that would just be the PLL0
>> AUXCLK. On most of the other SoCs, it would be the PLL AUXCLK plus one
>> LPSC clock. The AUXCLKs are easy because they are just a simple gate
>> from the oscillator. The LPSC clocks are a bit more tricky because they
>> have a complex sequence for turning on. Furthermore, on DM646X, we need
>> the whole PLL up to SYSCLK3 plus one LPSC clock, so things get a bit
>> messy there.
> 
> Things might change in the context of work being done here by Bartosz
> for converting clocks to early platform devices.
> 
> But, keeping that development aside for a moment: I think this means the
> PLLs and PSCs need to be CLK_OF_DECLARE(). What we can have as platform
> devices are clocks that are not in the path to get timer clock working
> (like CFGCHIP clocks).

CLK_OF_DECLARE() only matters on DA850. None of the other SoCs use device
tree. And on DA850, the timer0 clock is just the PLL0 AUXCLK, so PSCs can
still be platform devices there. And in fact, one of the PSC clocks on
DA850 depends on async3, which is a CFGCHIP clock, so if we made the PSCs
CLK_OF_DECLARE(), then we also have to make at least the async3 CFGCHIP
clock CLK_OF_DECLARE(). But, like I said, I think that can be avoided by
leaving the PSC clocks as a platform device on DA850 (and DA830).

For everything else, we need the legacy board file equivalent of
CLK_OF_DECLARE(), which is basically what I had here in v5 of the
series.

So, if we want this to keep moving before the if/when of Bartosz's
early platform device stuff, I'm thinking that I will make the PLL
and PSC drivers loadable with or without a platform device and let
each SoC pick which one it should use.