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

[Kunihiko Hayashi]

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