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

[Jon Hunter]

Hi Rajendra,

On 06/10/16 09:43, Rajendra Nayak wrote:
> On 10/06/2016 01:55 PM, Jon Hunter wrote:
> > Hi Rajendra,
> >
> > On 06/10/16 07:04, Rajendra Nayak wrote:
> > > On 09/20/2016 03:58 PM, 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.
> > >
> > > Hey Jon, so does this RFC provide a way to just specify multiple Powerdomains
> > > for a device (which then will *all* be powered on/off together) or does
> > > it also provide for more granular control of these powerdomains?
> >
> > Only to specify multiple power-domains for a device and not the later.
> >
> > > The above statement seems to suggest you would need more granular control
> > > of these powerdomains (like keeping XUSBA off in case superspeed it not
> > > needed) but I can't seem to figure out how you achieve it with this series.
> >
> > It is an interesting point but today we have always kept the superspeed
> > partition on if the device is configured for superspeed regardless of
> > what is actually connected. I will check to see if the h/w would allow
> > us to turn it off if a non-superspeed device is in use but I did not
> > think so.
> >
> > Do you have any interesting use-cases that would make use of this or
> > require other such enhancements?
>
> We do have atleast a few devices which need to control multiple power domains,
> I will need to look more to see if any of them can be controlled individually.
> The downstream code we have models these (powerdomains) as regulators and
> the drivers hence have individual control on each (specifying multiple -supply's
> in DT)

Were you able to check to see if you need to have individual control for 
the power-domains?

Cheers
Jon

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