linux-kernel - Re: [PATCH] arm64: dts: marvell: armada-37xx: Set linux,pci-domain to zero

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Date:   Thu, 15 Apr 2021 10:36:40 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Marek Behún <marek.behun@....cz>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: marvell: armada-37xx: Set linux,pci-domain
 to zero

On Tuesday 13 April 2021 13:17:29 Rob Herring wrote:
> On Mon, Apr 12, 2021 at 7:41 AM Pali Rohár <pali@...nel.org> wrote:
> >
> > Since commit 526a76991b7b ("PCI: aardvark: Implement driver 'remove'
> > function and allow to build it as module") PCIe controller driver for
> > Armada 37xx can be dynamically loaded and unloaded at runtime. Also driver
> > allows dynamic binding and unbinding of PCIe controller device.
> >
> > Kernel PCI subsystem assigns by default dynamically allocated PCI domain
> > number (starting from zero) for this PCIe controller every time when device
> > is bound. So PCI domain changes after every unbind / bind operation.
> 
> PCI host bridges as a module are relatively new, so seems likely a bug to me.

Why a bug? It is there since 5.10 and it is working.

> > Alternative way for assigning PCI domain number is to use static allocated
> > numbers defined in Device Tree. This option has requirement that every PCI
> > controller in system must have defined PCI bus number in Device Tree.
> 
> That seems entirely pointless from a DT point of view with a single PCI bridge.

If domain id is not specified in DT then kernel uses counter and assigns
counter++. So it is not pointless if we want to have stable domain id.

> > Armada 37xx has only one PCIe controller, so assign for it PCI domain 0 in
> > Device Tree.
> >
> > After this change PCI domain on Armada 37xx is always zero, even after
> > repeated unbind and bind operations.
> >
> > Signed-off-by: Pali Rohár <pali@...nel.org>
> > Fixes: 526a76991b7b ("PCI: aardvark: Implement driver 'remove' function and allow to build it as module")
> > ---
> >  arch/arm64/boot/dts/marvell/armada-37xx.dtsi | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm64/boot/dts/marvell/armada-37xx.dtsi b/arch/arm64/boot/dts/marvell/armada-37xx.dtsi
> > index 7a2df148c6a3..f02058ef5364 100644
> > --- a/arch/arm64/boot/dts/marvell/armada-37xx.dtsi
> > +++ b/arch/arm64/boot/dts/marvell/armada-37xx.dtsi
> > @@ -495,6 +495,7 @@
> >                                         <0 0 0 2 &pcie_intc 1>,
> >                                         <0 0 0 3 &pcie_intc 2>,
> >                                         <0 0 0 4 &pcie_intc 3>;
> > +                       linux,pci-domain = <0>;
> >                         max-link-speed = <2>;
> >                         phys = <&comphy1 0>;
> >                         pcie_intc: interrupt-controller {
> > --
> > 2.20.1
> >