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Subject: Re: [PATCH 1/6] dt/bindings: adjust bindings for Layerscape SCFG MSI
To: Minghuan Lian <Minghuan.Lian@nxp.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org
References: <1477398945-22774-1-git-send-email-Minghuan.Lian@nxp.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>,
        Stuart Yoder <stuart.yoder@nxp.com>, Yang-Leo Li <leoyang.li@nxp.com>,
        Scott Wood <scott.wood@nxp.com>, Shawn Guo <shawnguo@kernel.org>,
        Mingkai Hu <mingkai.hu@nxp.com>
From: Robin Murphy <robin.murphy@arm.com>
Message-ID: <0416d929-dfef-da09-8d9a-d1db8575afef@arm.com>
Date: Tue, 25 Oct 2016 14:01:16 +0100
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On 25/10/16 13:35, Minghuan Lian wrote:
> 1. The different version of a SoC may have different MSI
> implementation. But compatible "fsl,<soc-name>-msi" can not describe
> the SoC version.

Can't it?

	compatible = "fsl-ls1043a-rev11-msi";

Oh, I guess it can!

Joking aside, if there are multiple versions of a piece of hardware
which require *different* treatment by drivers, then it is obviously
wrong to use the same compatible string because *they are not compatible*.

> The MSI driver will use SoC match interface to get
> SoC type and version instead of compatible string. So all MSI node
> can use the common compatible "fsl,ls-scfg-msi" and the original
> compatible is unnecessary.

If there is some common level of functionality that *all* variants
support without the driver having to know which one is which, then there
might be some sense in having an additional common compatible to
represent that level of functionality, e.g.

	compatible = "fsl-ls1043a-rev11-msi", "fsl,ls-scfg-msi";

But if, say, new variants turn out to have less functionality, rather
than more, then there's probably not much point, and we should stick to
specific, accurate, compatible strings.

DT is not specific to a kernel version, nor even to Linux. A string
which triggers some board-specific magic in a specific version of a
Linux driver does not describe the hardware.

Robin.

> 2. Layerscape SoCs may have one or several MSI controllers.
> In order to increase MSI interrupt number of a PCIe, the patch
> moves all MSI node into the parent node "msi-controller". So a
> PCIe can request MSI from all the MSI controllers.
> 
> Signed-off-by: Minghuan Lian <Minghuan.Lian@nxp.com>
> ---
>  .../interrupt-controller/fsl,ls-scfg-msi.txt       | 57 +++++++++++++++++++---
>  1 file changed, 49 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/interrupt-controller/fsl,ls-scfg-msi.txt b/Documentation/devicetree/bindings/interrupt-controller/fsl,ls-scfg-msi.txt
> index 9e38949..29f95fd 100644
> --- a/Documentation/devicetree/bindings/interrupt-controller/fsl,ls-scfg-msi.txt
> +++ b/Documentation/devicetree/bindings/interrupt-controller/fsl,ls-scfg-msi.txt
> @@ -1,18 +1,28 @@
>  * Freescale Layerscape SCFG PCIe MSI controller
>  
> +Layerscape SoCs may have one or multiple MSI controllers.
> +Each MSI controller must be showed as a child node.
> +
>  Required properties:
>  
> -- compatible: should be "fsl,<soc-name>-msi" to identify
> -	      Layerscape PCIe MSI controller block such as:
> -              "fsl,1s1021a-msi"
> -              "fsl,1s1043a-msi"
> +- compatible: should be "fsl,ls-scfg-msi"
> +- #address-cells: must be 2
> +- #size-cells: must be 2
> +- ranges: allows valid 1:1 translation between child's address space and
> +	  parent's address space
>  - msi-controller: indicates that this is a PCIe MSI controller node
> +
> +Required child node:
> +A child node must exist to represent the MSI controller.
> +The following are properties specific to those nodes:
> +
>  - reg: physical base address of the controller and length of memory mapped.
>  - interrupts: an interrupt to the parent interrupt controller.
>  
>  Optional properties:
>  - interrupt-parent: the phandle to the parent interrupt controller.
>  
> +Notes:
>  This interrupt controller hardware is a second level interrupt controller that
>  is hooked to a parent interrupt controller: e.g: ARM GIC for ARM-based
>  platforms. If interrupt-parent is not provided, the default parent interrupt
> @@ -22,9 +32,40 @@ MSI controller node
>  
>  Examples:
>  
> -	msi1: msi-controller@1571000 {
> -		compatible = "fsl,1s1043a-msi";
> -		reg = <0x0 0x1571000 0x0 0x8>,
> +	msi: msi-controller {
> +		compatible = "fsl,ls-scfg-msi";
> +		#address-cells = <2>;
> +		#size-cells = <2>;
> +		ranges;
>  		msi-controller;
> -		interrupts = <0 116 0x4>;
> +
> +		msi0@1580000 {
> +			reg = <0x0 0x1580000 0x0 0x10000>;
> +			interrupts = <0 116 0x4>,
> +				     <0 111 0x4>,
> +				     <0 112 0x4>,
> +				     <0 113 0x4>;
> +		};
> +
> +		msi1@1590000 {
> +			reg = <0x0 0x1590000 0x0 0x10000>;
> +			interrupts = <0 126 0x4>,
> +				     <0 121 0x4>,
> +				     <0 122 0x4>,
> +				     <0 123 0x4>;
> +		};
> +
> +		msi2@15a0000 {
> +			reg = <0x0 0x15a0000 0x0 0x10000>;
> +			interrupts = <0 160 0x4>,
> +				     <0 155 0x4>,
> +				     <0 156 0x4>,
> +				     <0 157 0x4>;
> +		};
> +	};
> +
> +	pcie@3400000 {
> +			...
> +			msi-parent = <&msi>;
> +			...
>  	};
>