Devicetree

* Re: [PATCH v2 2/4] dt-bindings: Add TI SCI PM Domains
From: Dave Gerlach @ 2016-11-14 19:20 UTC (permalink / raw)
  To: Ulf Hansson, Rob Herring
  Cc: Nishanth Menon, devicetree@vger.kernel.org, Santosh Shilimkar,
	linux-pm@vger.kernel.org, Kevin Hilman, Sudeep Holla,
	Rafael J . Wysocki, linux-kernel@vger.kernel.org, Jon Hunter,
	Tero Kristo, Russell King, Keerthy,
	linux-arm-kernel@lists.infradead.org
In-Reply-To: <CAPDyKFofZdFfGA8gbS9FJxAX5Ub-s8yZWDcNVOgwiEBpho4oyw@mail.gmail.com>

Hi,
On 11/11/2016 06:34 AM, Ulf Hansson wrote:
> On 10 November 2016 at 20:56, Dave Gerlach <d-gerlach@ti.com> wrote:
>> Rob, Ulf, Jon,
>>
>> On 10/27/2016 08:15 AM, Dave Gerlach wrote:
>>>
>>> +Jon
>>> On 10/26/2016 04:59 PM, Rob Herring wrote:
>>>>
>>>> On Mon, Oct 24, 2016 at 12:00 PM, Kevin Hilman <khilman@baylibre.com>
>>>> wrote:
>>>>>
>>>>> Dave Gerlach <d-gerlach@ti.com> writes:
>>>>>
>>>>>> Hi,
>>>>>> On 10/21/2016 01:48 PM, Kevin Hilman wrote:
>>>>>>>
>>>>>>> Dave Gerlach <d-gerlach@ti.com> writes:
>>>>>>>
>>>>>>>> Add a generic power domain implementation, TI SCI PM Domains, that
>>>>>>>> will hook into the genpd framework and allow the TI SCI protocol to
>>>>>>>> control device power states.
>>>>>>>>
>>>>>>>> Also, provide macros representing each device index as understood
>>>>>>>> by TI SCI to be used in the device node power-domain references.
>>>>>>>> These are identifiers for the K2G devices managed by the PMMC.
>>>>>>>>
>>>>>>>> Signed-off-by: Nishanth Menon <nm@ti.com>
>>>>>>>> Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
>>>>>>>> ---
>>>>>>>>  .../devicetree/bindings/soc/ti/sci-pm-domain.txt   | 54
>>>>>>>> +++++++++++++
>>>>>>>>  MAINTAINERS                                        |  2 +
>>>>>>>>  include/dt-bindings/genpd/k2g.h                    | 90
>>>>>>>> ++++++++++++++++++++++
>>>>>>>>  3 files changed, 146 insertions(+)
>>>>>>>>  create mode 100644
>>>>>>>> Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
>>>>>>>>  create mode 100644 include/dt-bindings/genpd/k2g.h
>>>>>>>>
>>>>>>>> diff --git
>>>>>>>> a/Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
>>>>>>>> b/Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
>>>>>>>> new file mode 100644
>>>>>>>> index 000000000000..32f38a349656
>>>>>>>> --- /dev/null
>>>>>>>> +++ b/Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
>>>>>>>> @@ -0,0 +1,54 @@
>>>>>>>> +Texas Instruments TI-SCI Generic Power Domain
>>>>>>>> +---------------------------------------------
>>>>>>>> +
>>>>>>>> +Some TI SoCs contain a system controller (like the PMMC, etc...)
>>>>>>>> that is
>>>>>>>> +responsible for controlling the state of the IPs that are present.
>>>>>>>> +Communication between the host processor running an OS and the
>>>>>>>> system
>>>>>>>> +controller happens through a protocol known as TI-SCI [1]. This pm
>>>>>>>> domain
>>>>>>>> +implementation plugs into the generic pm domain framework and makes
>>>>>>>> use of
>>>>>>>> +the TI SCI protocol power on and off each device when needed.
>>>>>>>> +
>>>>>>>> +[1] Documentation/devicetree/bindings/arm/keystone/ti,sci.txt
>>>>>>>> +
>>>>>>>> +PM Domain Node
>>>>>>>> +==============
>>>>>>>> +The PM domain node represents the global PM domain managed by the
>>>>>>>> PMMC,
>>>>>>>> +which in this case is the single implementation as documented by the
>>>>>>>> generic
>>>>>>>> +PM domain bindings in
>>>>>>>> Documentation/devicetree/bindings/power/power_domain.txt.
>>>>>>>> +
>>>>>>>> +Required Properties:
>>>>>>>> +--------------------
>>>>>>>> +- compatible: should be "ti,sci-pm-domain"
>>>>>>>> +- #power-domain-cells: Must be 0.
>>>>>>>> +- ti,sci: Phandle to the TI SCI device to use for managing the
>>>>>>>> devices.
>>>>>>>>
>>>>>>>> +Example:
>>>>>>>> +--------------------
>>>>>>>> +k2g_pds: k2g_pds {
>>>>>>>
>>>>>>>
>>>>>>> should use generic name like "power-contoller", e.g. k2g_pds:
>>>>>>> power-controller
>>>>>>
>>>>>>
>>>>>> Ok, that makes more sense.
>>>>>>
>>>>>>>
>>>>>>>> +        compatible = "ti,sci-pm-domain";
>>>>>>>> +        #power-domain-cells = <0>;
>>>>>>>> +        ti,sci = <&pmmc>;
>>>>>>>> +};
>>>>>>>> +
>>>>>>>> +PM Domain Consumers
>>>>>>>> +===================
>>>>>>>> +Hardware blocks that require SCI control over their state must
>>>>>>>> provide
>>>>>>>> +a reference to the sci-pm-domain they are part of and a unique
>>>>>>>> device
>>>>>>>> +specific ID that identifies the device.
>>>>>>>> +
>>>>>>>> +Required Properties:
>>>>>>>> +--------------------
>>>>>>>> +- power-domains: phandle pointing to the corresponding PM domain
>>>>>>>> node.
>>>>>>>> +- ti,sci-id: index representing the device id to be passed oevr SCI
>>>>>>>> to
>>>>>>>> +        be used for device control.
>>>>>>>
>>>>>>>
>>>>>>> This ID doesn't look right.
>>>>>>>
>>>>>>> Why not use #power-domain-cells = <1> and pass the index in the DT?
>>>>>>> ...
>>>>
>>>>
>>>> Exactly. ti,sci-id is a NAK for me.
>>>
>>>
>>> I was told not to use the onecell during v1 discussion. I agree this would
>>> be
>>> ideal but I cannot due to what the bindings represent, the phandle
>>> parameter is
>>> an index into a list of genpds, whereas we need an actual ID number we can
>>> use
>>> and I do not have the ability to get that from the phandle.
>>>
>>> @Ulf/Jon, is there any hope of bringing back custom xlate functions for
>>> genpd
>>> providers? I don't have a good background on why it was even removed. I
>>> can
>>> maintain a single genpd for all devices but I need a way to parse this ID,
>>> whether it's from a separate property or a phandle. It is locked now to
>>> indexing
>>> into a list of genpds but I need additional per device information for
>>> devices
>>> bound to a genpd and I need either a custom parameter or the ability to
>>> parse
>>> the phandle myself.
>>>
>>
>> Any comments here? The meaning of the phandle onecell is fixed in the genpd
>> framework so I'm not sure how we want to move forward with this, I need to
>> pass a power domain ID to the genpd driver, and if this shouldn't be a new
>> property I'm not sure what direction we should take.
>>
>> Regards,
>> Dave
>>
>>
>>>>
>>>>>>>
>>>>>>>> +See dt-bindings/genpd/k2g.h for the list of valid identifiers for
>>>>>>>> k2g.
>>>>>>>> +
>>>>>>>> +Example:
>>>>>>>> +--------------------
>>>>>>>> +uart0: serial@02530c00 {
>>>>>>>> +   compatible = "ns16550a";
>>>>>>>> +   ...
>>>>>>>> +   power-domains = <&k2g_pds>;
>>>>>>>> +   ti,sci-id = <K2G_DEV_UART0>;
>>>>>>>
>>>>>>>
>>>>>>> ... like this:
>>>>>>>
>>>>>>>      power-domains = <&k2g_pds K2G_DEV_UART0>;
>>>>>>
>>>>>>
>>>>>> That's how I did it in version one actually. I was able to define my
>>>>>> own xlate function to parse the phandle and get that index, but Ulf
>>>>>> pointed me to this series by Jon Hunter [1] that simplified genpd
>>>>>> providers and dropped the concept of adding your own xlate. This locks
>>>>>> the onecell approach to using a fixed static array of genpds that get
>>>>>> indexed into (without passing the index to the provider, just the
>>>>>> genpd that's looked up), which doesn't fit our usecase, as we don't
>>>>>> want a 1 to 1 genpd to device mapping based on the comments provided
>>>>>> in v1. Now we just use the genpd device attach/detach hooks to parse
>>>>>> the sci-id and then use it in the genpd device start/stop hooks.
>>>>
>>>>
>>>> I have no idea what any of this means. All sounds like driver
>>>> architecture, not anything to do with bindings.
>>>
>>>
>>> This was a response to Kevin, not part of binding description.
>>>
>>>>
>>>>>
>>>>> Ah, right.  I remember now.  This approach allows you to use a single
>>>>> genpd as discussed earlier.
>>>>>
>>>>> Makes sense now, suggestion retracted.
>>>>
>>>>
>>>> IIRC, the bindings in Jon's case had a node for each domain and didn't
>>>> need any additional property.
>>>
>>>
>>> Yes but we only have one domain and index into it, not into a list of
>>> domains,
>
> Exactly. And this my main point as well. We are not talking about a
> domain property but a device property.
>
>>> so the additional property is solving a different problem.
>
> Yes.
>
> Perhaps you could try to elaborate about what the TI SCI ID really
> represents for the device, as to help Rob understand the bigger
> picture?
>
> To me, the TI SCI ID, is similar to a "conid" for any another "device
> resource" (like clock, pinctrl, regulator etc) which we can describe
> in DT and assign to a device node. The only difference here, is that
> we don't have common API to fetch the resource (like clk_get(),
> regulator_get()), but instead we fetches the device's resource from
> SoC specific code, via genpd's device ->attach() callback.

Thanks for the response. Yes, you've pretty much hit it on the head. It 
is not an index into a list of genpds but rather identifies the device 
*within* a single genpd. It is a property specific to each device that 
resides in a ti-sci-genpd, not a mapping describing which genpd the 
device belongs to. The generic power domain binding is concerned with 
mapping the device to a specific genpd, which is does fine for us, but 
we have a sub mapping for devices that exist inside a genpd which, we 
must describe as well, hence the ti,sci-id.

Regards,
Dave

>
> Hope that helps.
>
> Kind regards
> Uffe
>

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