Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Wed, 3 May 2017 10:54:33 +0200 | Subject | Re: [RFC PATCH 0/4] PM / Domains: Add support for explicit control of PM domains |
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Hi Ulf,
On Wed, May 3, 2017 at 8:43 AM, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > On Wed, Apr 26, 2017 at 11:55 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote: >> On 26 April 2017 at 11:17, Geert Uytterhoeven <geert@linux-m68k.org> wrote: >>> On Wed, Apr 26, 2017 at 11:04 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote: >>>> On 26 April 2017 at 10:06, Geert Uytterhoeven <geert@linux-m68k.org> wrote: >>>>> On Tue, Apr 25, 2017 at 9:34 PM, Ulf Hansson <ulf.hansson@linaro.org> 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.
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
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
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