linux-kernel - Re: [PATCH 4/4] arm64: dts: uniphier: Add NX1 SoC and boards support

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Message-ID: <fdf94c6b-0293-5dd0-1717-176d1a2056de@socionext.com>
Date:   Thu, 27 Oct 2022 20:58:07 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Arnd Bergmann <arnd@...db.de>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Olof Johansson <olof@...om.net>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     soc@...nel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] arm64: dts: uniphier: Add NX1 SoC and boards support

On 2022/10/27 20:28, Arnd Bergmann wrote:
> On Thu, Oct 27, 2022, at 13:19, Kunihiko Hayashi wrote:
>> On 2022/10/27 19:01, Arnd Bergmann wrote:
>>> On Thu, Oct 27, 2022, at 06:51, Kunihiko Hayashi wrote:
> 
>>>> +			#interrupt-cells = <1>;
>>>> +			interrupt-names = "dma", "msi";
>>>> +			interrupts = <GIC_SPI 84 IRQ_TYPE_LEVEL_HIGH>,
>>>> +				     <GIC_SPI 85 IRQ_TYPE_LEVEL_HIGH>;
>>>> +			interrupt-map-mask = <0 0 0 7>;
>>>> +			interrupt-map = <0 0 0 1 &pcie_intc 0>,	/* INTA */
>>>> +					<0 0 0 2 &pcie_intc 1>,	/* INTB */
>>>> +					<0 0 0 3 &pcie_intc 2>,	/* INTC */
>>>> +					<0 0 0 4 &pcie_intc 3>;	/* INTD */
>>>> +			phy-names = "pcie-phy";
>>>> +			phys = <&pcie_phy>;
>>>> +
>>>> +			pcie_intc: legacy-interrupt-controller {
>>>> +				interrupt-controller;
>>>> +				#interrupt-cells = <1>;
>>>> +				interrupt-parent = <&gic>;
>>>> +				interrupts = <GIC_SPI 86
>>> IRQ_TYPE_LEVEL_HIGH>;
>>>> +			};
>>>> +		};
>>>
>>> Shouldn't there be an "msi-map" or "msi-parent" property pointing at
>>> the GIC?
>>
>> Since Designware PCIe receives an interrupt from GIC with interrupt-name
> "msi"
>> and passes the interrupt to the linear irq domain corresponding to MSI,
>> I think there is neither "msi-map" nor "msi-parent" properties.
> 
> Usually, you have the choice to use either the built-in
> MSI logic of the PCIe controller, or the one built into the
> GIC itself, assuming you have a modern enough GIC implemetation.

I recognize ITS built into GICv3 can perform the parent of MSI.

> Using the GIC is preferred here, because otherwise you lose
> all the benefits that MSIs offer, regarding latency and CPU
> affinity.

I understand, however, unfortunately GIC-ITS (or something alternative)
isn't supported in this SoC, so I think it is difficult to use the GIC
itself as msi-parent.

Thank you,

---
Best Regards
Kunihiko Hayashi