linux-kernel - Re: [PATCH 1/2] dt-bindings: irqchip: Introduce TISCI Interrupt router bindings

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Date:   Sat, 6 Oct 2018 11:29:29 -0500
From:   Nishanth Menon <nm@...com>
To:     Lokesh Vutla <lokeshvutla@...com>
CC:     Tero Kristo <t-kristo@...com>, <tglx@...utronix.de>,
        <jason@...edaemon.net>, <marc.zyngier@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Device Tree Mailing List <devicetree@...r.kernel.org>,
        Linux ARM Mailing List <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, Sekhar Nori <nsekhar@...com>
Subject: Re: [PATCH 1/2] dt-bindings: irqchip: Introduce TISCI Interrupt
 router bindings

On 12:58-20181006, Lokesh Vutla wrote:
> Add the DT binding documentation for Interrupt router driver.
> 
> Signed-off-by: Lokesh Vutla <lokeshvutla@...com>
> ---
>  .../interrupt-controller/ti,sci-intr.txt      | 83 +++++++++++++++++++
>  MAINTAINERS                                   |  1 +
>  2 files changed, 84 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/interrupt-controller/ti,sci-intr.txt
> 
> diff --git a/Documentation/devicetree/bindings/interrupt-controller/ti,sci-intr.txt b/Documentation/devicetree/bindings/interrupt-controller/ti,sci-intr.txt
> new file mode 100644
> index 000000000000..681ca53cc5fb
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/interrupt-controller/ti,sci-intr.txt
> @@ -0,0 +1,83 @@
> +Texas Instruments K3 Interrupt Router
> +=====================================
> +
> +The Interrupt Router (INTR) module provides a mechanism to mux M
> +interrupt inputs to N interrupt outputs, where all M inputs are selectable
> +to be driven per N output. There is one register per output (MUXCNTL_N) that
> +controls the selection.
> +
> +
> +                                 Interrupt Router
> +                             +----------------------+
> +                             |  Inputs     Outputs  |
> +        +-------+            | +------+             |
> +        | GPIO  |----------->| | irq0 |             |       Host IRQ
> +        +-------+            | +------+             |      controller
> +                             |    .        +-----+  |      +-------+
> +        +-------+            |    .        |  0  |  |----->|  GIC  |
> +        | INTA  |----------->|    .        +-----+  |      +-------+
> +        +-------+            |    .          .      |
> +                             | +------+      .      |
> +                             | | irqM |    +-----+  |
> +                             | +------+    |  N  |  |
> +                             |             +-----+  |
> +                             +----------------------+
> +
> +Configuration of these MUXCNTL_N registers is done by a system controller
> +(like the Device Memory and Security Controller on K3 AM654 SoC). System
> +controller will keep track of the used and unused registers within the Router.
> +Driver should request the system controller to get the range of GIC IRQs
> +assigned to the requesting hosts. It is the drivers responsibility to keep
> +track of GIC IRQs.
> +
> +Communication between the host processor running an OS and the system
> +controller happens through a protocol called TI System Control Interface
> +(TISCI protocol). For more details refer:
> +Documentation/devicetree/bindings/arm/keystone/ti,sci.txt
> +
> +TISCI Interrupt Router Node:
> +----------------------------
> +- compatible:		Must be "ti,sci-intr".
> +- interrupt-controller:	Identifies the node as an interrupt controller
> +- #interrupt-cells:	Specifies the number of cells needed to encode an
> +			interrupt source. The value should be 3.
> +			First cell should contain the TISCI device ID of source
> +			Second cell should contain the interrupt source offset
> +			within the device
> +			Third cell specifies the trigger type as defined
> +			in interrupts.txt in this directory.
> +- interrupt-parent:	phandle of irq parent for TISCI intr. The parent must
> +			use the same interrupt-cells format as GIC.
> +- ti,sci:		Phandle to TI-SCI compatible System controller node.
> +- ti,sci-dst-id:	TISCI device ID of the destination IRQ controller.
> +- ti,sci-rm-range-girq:	Tuple corresponding to unique TISCI resource type that
> +			defines the dst host irq ranges assigned to this
> +			interrupt router from this host context.
> +			Tuple should be of format <type subtype>.
> +

Rob, DT maintainers,

I'd like a feedback from DT maintainers on this 'range' topic.

TISCI Firmware [1] currently seems to define a type corresponding to a
device ID[2]. in AM6 device, for example, this is different, however
have a 1 to 1 correspondence. However, there is expectation that type will
end up as device ID in a future SoC.

While this is subject to much debate internally, I'd like some feedback if this
is OK from Device tree representation - it is true that Firmware does
look at it as type, however in some future SoC, it could be that the
values themselves may correspond one to one with a device id -> The
original wish was that types might be something reusable across SoCs,
but that is turning out to be more of a theoretical wish than any thing
practical.

[1]http://software-dl.ti.com/tisci/esd/latest/5_soc_doc/am6x/resasg_types.html
[2]http://software-dl.ti.com/tisci/esd/latest/5_soc_doc/am6x/devices.html
-- 
Regards,
Nishanth Menon