Re: [RFC PATCH 0/3] PM / Domains: Add support for devices that require multiple domains

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Jon,

On Tue, Feb 28, 2017 at 4:18 PM, Jon Hunter <jonathanh@nvidia.com> wrote:
> On 20/09/16 11:28, Jon Hunter wrote:
>> The Tegra124/210 XUSB subsystem (that consists of both host and device
>> controllers) is partitioned across 3 PM domains which are:
>> - XUSBA: Superspeed logic (for USB 3.0)
>> - XUSBB: Device controller
>> - XUSBC: Host controller
>>
>> These power domains are not nested and can be powered-up and down
>> independently of one another. In practice different scenarios require
>> different combinations of the power domains, for example:
>> - Superspeed host: XUSBA and XUSBC
>> - Superspeed device: XUSBA and XUSBB
>>
>> Although it could be possible to logically nest both the XUSBB and XUSBC
>> domains under the XUSBA, superspeed may not always be used/required and
>> so this would keep it on unnecessarily.
>>
>> Given that Tegra uses device-tree for describing the hardware, it would
>> be ideal that the device-tree 'power-domains' property for generic PM
>> domains could be extended to allow more than one PM domain to be
>> specified. For example, define the following the Tegra210 xHCI device ...
>>
>>       usb@70090000 {
>>               compatible = "nvidia,tegra210-xusb";
>>               ...
>>               power-domains = <&pd_xusbhost>, <&pd_xusbss>;
>>       };
>>
>> This RFC extends the generic PM domain framework to allow a device to
>> define more than one PM domain in the device-tree 'power-domains'
>> property.
>
> I wanted to kick this thread again now in the new year and see if there
> is still some interest in pursuing this?
>
> There is still very much a need from a Tegra perspective. I have put all
> those who responded on TO.
>
> I know that a lot of time has passed since we discuss this and so if you
> are scratching your head wondering what I am harping on about,
> essentially with this RFC I was looking for a way to support devices
> that require multiple power domains where the domains do not have a
> parent-child relationship and so not are nested in anyway.
>
> If you need me to elaborate on the need for this, I am happy to do this.
> My take away from when we discussed this last year, was that there was a
> need for this.

It definitely makes sense to me, as the "power-domains" DT binding is not
limited to plain "power areas", but may refer to clock domains, too
(cfr. the Linux "PM Domain" notion).

For my (Renesas) use case, we have devices that are part of both a power
area and a clock domain. Currently this is handled by the power area driver
calling into the clock driver.

Thanks!

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