Re: [RFC PATCH 0/4] PM / Domains: Add support for explicit control of PM domains

From: Geert Uytterhoeven
Date: Wed May 03 2017 - 04:54:44 EST

Hi Ulf,

On Wed, May 3, 2017 at 8:43 AM, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> On Wed, Apr 26, 2017 at 11:55 AM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>> On 26 April 2017 at 11:17, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>>> On Wed, Apr 26, 2017 at 11:04 AM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>>>> On 26 April 2017 at 10:06, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>>>>> On Tue, Apr 25, 2017 at 9:34 PM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>>>>>> However, we currently know about at least two different SoCs that need
>>>>>> this. Perhaps we can extend the below list to justify adding a new
>>>>>> framework/APIs. Something along the lines what you propose in $subject
>>>>>> patchset.
>>>>>> 1) Nvidia; to solve the USB super-speed host/device problem.
>>>>>> 2) QCOM, which has pointed to several cases where the PM topology is
>>>>>> laid out like devices having two PM domains..
>>>>>> 3?) I don't fully remember - but I think Geert also pointed to some
>>>>>> examples where a device could reside in a clock domain but also in
>>>>>> power domain for a Renesas SoC!?
>>>>>> 4) ?
>>>>> Most Renesas SoCs have module clocks, which we model as a clock domain.
>>>>> Some Renesas SoCs have power domains for CPUs, others have them for
>>>>> devices as well.
>>>>> As we always provide a virtual "always-on" power domain in the power domain
>>>>> controller, all devices can refer to it using "power-domains" properties,
>>>>> and the driver for the power domain controller can just forward the clock
>>>>> domain operations to the clock driver.
>>>> Okay, thanks for clarifying this.
>>>> Thinking about this as bit more, when I realized that *if* we would
>>>> add a new PM domain framework for explicit control of PM domains, that
>>>> would mean you need to deploy support for that in the drivers.
>>> Correct. And we have to update DT bindings and DTS.
>>>> On the other hand, as you anyway would need to change the drivers, you
>>>> could instead deploy clock support in the drivers, which would avoid
>>>> using the clock domain. In that way, you could still stay with one PM
>>>> domain pointer per device, used to control the power domains instead.
>>>> Right? Or would that have other implications?
>>> That's exactly what we're doing already.
>> No really, but perhaps I was not clear enough.
>> Currently you deploy only runtime PM support in the driver and don't
>> do any clk_get() etc. Then you have a PM domain (genpd) attached to

Note that drivers that care about clock properties do use clk_get().
E.g. an SPI controller driver needs to know the clock rate to program
its internal divider to drive external SPI slaves.

>> the device and makes use of genpd's device specific callbacks, in
>> struct gpd_dev_ops ->start|stop(), which allows you to control clocks
>> for each device. Of course this is perfectly okay.
> OK.



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds