On 02/09/17 10:52, Frank Rowand wrote:
> On 02/09/17 07:17, Rob Herring wrote:
>> On Tue, Jan 24, 2017 at 12:05 PM, Rob Herring <robh+dt@xxxxxxxxxx> wrote:
>>> On Tue, Jan 24, 2017 at 12:36 AM, Frank Rowand <frowand.list@xxxxxxxxx> wrote:
>>>> Hi Stephen,
>>>>
>>>> Sorry I did not get to v1 and v2 in a timely manner.
>>>>
>>>>
>>>> On 01/23/17 12:48, Stephen Boyd wrote:
>>>>> Platforms like 96boards have a standardized connector/expansion
>>>>> slot that exposes signals like GPIOs to expansion boards in an
>>>>> SoC agnostic way. We'd like the DT overlays for the expansion
>>>>> boards to be written once without knowledge of the SoC on the
>>>>> other side of the connector. This avoids the unscalable
>>>>> combinatorial explosion of a different DT overlay for each
>>>>> expansion board and SoC pair.
>>>>>
>>>>> We need a way to describe the GPIOs routed through the connector
>>>>> in an SoC agnostic way. Let's introduce nexus property parsing
>>>>> into the OF core to do this. This is largely based on the
>>>>> interrupt nexus support we already have. This allows us to remap
>>>>> a phandle list in a consumer node (e.g. reset-gpios) through a
>>>>> connector in a generic way (e.g. via gpio-map). Do this in a
>>>>> generic routine so that we can remap any sort of variable length
>>>>> phandle list.
>>>>>
>>>>> Taking GPIOs as an example, the connector would be a GPIO nexus,
>>>>> supporting the remapping of a GPIO specifier space to multiple
>>>>> GPIO providers on the SoC. DT would look as shown below, where
>>>>> 'soc_gpio1' and 'soc_gpio2' are inside the SoC, 'connector' is an
>>>>> expansion port where boards can be plugged in, and
>>>>> 'expansion_device' is a device on the expansion board.
>>>>>
>>>>> soc {
>>>>> soc_gpio1: gpio-controller1 {
>>>>> #gpio-cells = <2>;
>>>>> };
>>>>>
>>>>> soc_gpio2: gpio-controller2 {
>>>>> #gpio-cells = <2>;
>>>>> };
>>>>> };
>>>>>
>>>>> connector: connector {
>>>>> #gpio-cells = <2>;
>>>>> gpio-map = <0 0 &soc_gpio1 1 0>,
>>>>> <1 0 &soc_gpio2 4 0>,
>>>>> <2 0 &soc_gpio1 3 0>,
>>>>> <3 0 &soc_gpio2 2 0>;
>>>>> gpio-map-mask = <0xf 0x0>;
>>>>> gpio-map-pass-thru = <0x0 0x1>
>>>>> };
>>>>>
>>>>> expansion_device {
>>>>> reset-gpios = <&connector 2 GPIO_ACTIVE_LOW>;
>>>>> };
>>>>
>>>> The how to architect connectors and plugs threads fell asleep before
>>>> coming to a resolution. We need to revive that discussion.
>>>>
>>>> One of the concepts of the plug and connector architecture is that
>>>> a main board may contain multiple connectors of the same type (or
>>>> different types, but the same type is sufficient for this discussion).
>>>>
>>>> The node describing the card that plugs into one of the connectors
>>>> does not know the phandle of the connector it is going to be
>>>> connected to. Some other mechanism is provided to allow a card
>>>> to be plugged into any of the available connectors. If there are
>>>> two identical cards plugged into two connectors, then both cards
>>>> have the same exact device tree node. But some mechanism will
>>>> exist to resolve (or "link") the two card nodes to the different
>>>> connector nodes.
>>>>
>>>> As a result of this, in the above example the reset-gpios property
>>>> in the node 'expansion_device' can not contain '&connector'. The
>>>> concept of &connector belongs to the entire expansion_device node,
>>>> not to individual properties within the node.
>>>
>>> I think this is easily solved with a connector having 2 halves and
>>> that we need to search parents for *-map properties. Inheriting from
>>> parents is a common pattern in DT though perhaps not walking the
>>> parents of a phandle. So we'd have something like this:
>>>
>>> base-connector-1 {
>>> gpio-map = ...
>>> connector {
>>> child {
>>> some-gpios = <&connector 1>;
>>> };
>>> };
>>> };
>>>
>>> base-connector-2 {
>>> gpio-map = ...
>>> connector {
>>> child {
>>> some-gpios = <&connector 1>;
>>> };
>>> };
>>> };
>>>
>>> Now, how we resolve that /connector from an overlay targets
>>> /base-connector-1 and /base-connector-2 is an orthogonal issue and one
>>> that's going to be connector specific (at least for probe-able
>>> connectors).
>>
>> Frank, any more comments on this? If not, I plan to apply this series.
>>
>> Rob
>
> Yes, how we resolve which connector a plug goes into is orthogonal.
>
> My objection is that the original example has a property in the
> plug node (that is, on the expansion board), directly referencing
> the connector node, instead of referencing a resource inside the
> connector node.
>
> In the original example, it would make more sense for the first
> item in the reset-gpios property to be &gpio-map or "gpio-map"
> instead of &connector.
My suggestion of &gpio-map or "gpio-map" was just shooting from
the hip. After going back to the DT connector thread, I have
a different answer of &gpio1 instead of &connector:
reset-gpios = <&gpio1 2 GPIO_ACTIVE_LOW>;
The full answer in more than changing &connector to &gpio1, see
below for the fuller dts.
I took David Gibson's initial socket / plug proposal[1], and added
in the gpios from Stephen's proposal.
[1] https://lkml.org/lkml/2016/7/18/332
----- Socket:
/dts-v1/;
/ {
compatible = "foo,oldboard";
ranges;
soc@... {
ranges;
mmio: mmio-bus@... {
#address-cells = <2>;
#size-cells = <2>;
ranges;
};
i2c: i2c@... {
};
intc: intc@... {
#interrupt-cells = <2>;
};
};
connectors {
widget1 {
compatible = "foo,widget-socket";
w1_irqs: irqs {
interrupt-controller;
#address-cells = <0>;
#interrupt-cells = <1>;
interrupt-map-mask = <0xffffffff>;
interrupt-map = <
0 &intc 7 0
1 &intc 8 0
>;
};
w1_gpio1: gpio1 {
#gpio-cells = <1>;
gpio-map = <0 &soc_gpio1 1 0>,
<1 &soc_gpio2 4 0>,
<2 &soc_gpio1 3 0>,
<3 &soc_gpio2 2 0>;
gpio-map-mask = <0xf>;
};
aliases = {
i2c = &i2c;
intc = &w1_irqs;
mmio = &mmio;
gpio1 = &w1_gpios1;
};
};
};
};
----- Expansion board:
/dts-v1/;
/plugin/ foo,widget-socket {
compatible = "foo,whirligig-widget";
};
expansion_device {
reset-gpios = <&gpio1 2 GPIO_ACTIVE_LOW>;
};
&i2c {
whirligig-controller@... {
...
interrupt-parent = <&widget-irqs>;
interrupts = <0>;
};
};
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