[RFC/RFT 2/6] clk: qcom: Add runtime support to handle clocks using PM clocks

[rnayak@codeaurora.org (Rajendra Nayak)]

On 04/28/2015 01:32 AM, Kevin Hilman wrote:
> Geert Uytterhoeven <geert@linux-m68k.org> writes:
>
>> On Fri, Apr 24, 2015 at 12:58 PM, Rajendra Nayak <rnayak@codeaurora.org> wrote:
>>>> Second, I want to see less users of pm_clk_add_notifier() since it's
>>>> not the proper/long-term way of how to assign PM domain pointers to a
>>>> device. Instead that shall be done at device registration point. In
>>>> your case while parsing the DT nodes and adding devices onto to their
>>>> buses.
>>>
>>> but these are devices which do not really have a controllable power
>>> domain, they just have controllable clocks.
>>>
>>>> Yes, I understand that it will requires quite some work to adopt to
>>>> this behaviour - but that how it shall be done.
>>>>
>>>> Finally, an important note, you don't need to use PM domains for these
>>>> devices at all and thus you don't need to fix what I propose. Instead
>>>> you only have to implement the runtime PM callbacks for each driver
>>>> and manage the clocks from there. That is probably also a easier
>>>> solution.
>>>
>>> But that would mean I repeat the same code in all drivers to do a
>>> clk_get/prepare/enable/disable/unprepare of the same "core" and "iface"
>>> clocks. I thought we have clock_ops.c just to avoid that (atleast up
>>> until we have a better way of doing it)
>>> And there are atleast a few architecture which have used it to avoid the
>>> duplication across all drivers (omap1/davinci/sh/keystone)
>>
>> At least for arm/shmobile, we're planning to move away from this, cfr.
>> http://www.spinics.net/lists/linux-sh/msg41114.html
>
> Just to clarify for Rajendra's sake...
>
> SH is moving away from the pm_clk_add_notifier(), but not duplicating
> the clk_get/prepare/enable/disable/unprepare across all the drivers.
>
> Rather, they're using a genpd to model the clock domain, and taking
> advantage of the pm_domain speciic attach callback to attach the PM
> clocks.
>
> This should work for qcom also assuming that these device nodes don't
> also need to belong to a different PM domain.

Thanks Kevin, I did look up the patches that Geert pointed me to, and
figured I can do something similar for qcom as well like you said.

There are 2 types of devices that I will need to handle, one which have
clocks and also a power switch to turn the power domain on/off (camera,
graphics, display), and others which only have clocks and no power
switch to control the power domain (serial, sdhc, i2c, spi).

I was already using genpd attach/detach to handle clocks for the
devices with a power switch and genpd on/off to turn the PD on and off.
I guess I can also control the rest of the devices the same way, just
that the genpd on/off for them would do nothing.
That way I don't have to use pm_clk_add_notifier() and can also
associate the power domain (with no on/off control) to devices
through DT (and there isn;t any duplication of code in the drivers)