linux-kernel - Re: [PATCH] ARM: dts: bcm2711-rpi-4-b: Fix pcie0's unit address

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Message-ID: <CAL_JsqJgf3SD51+_J=oNAOvMc9PmFNmuaVrisKkGV++JUzBwew@mail.gmail.com>
Date:   Mon, 30 Aug 2021 16:56:04 -0500
From:   Rob Herring <robh@...nel.org>
To:     nsaenzju@...hat.com
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devicetree@...r.kernel.org,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stefan Wahren <stefan.wahren@...e.com>
Subject: Re: [PATCH] ARM: dts: bcm2711-rpi-4-b: Fix pcie0's unit address

On Mon, Aug 30, 2021 at 11:45 AM <nsaenzju@...hat.com> wrote:
>
> On Mon, 2021-08-30 at 08:39 -0500, Rob Herring wrote:
> > On Mon, Aug 30, 2021 at 12:39:09PM +0200, Nicolas Saenz Julienne wrote:
> > > dtbs_check currently complains that:
> > >
> > > arch/arm/boot/dts/bcm2711-rpi-4-b.dts:220.10-231.4: Warning
> > > (pci_device_reg): /scb/pcie@...00000/pci@1,0: PCI unit address format
> > > error, expected "0,0"
> > >
> > > Unsurprisingly pci@0,0 is the right address, as illustrated by its reg
> > > property:
> > >
> > >     &pcie0 {
> > >             pci@0,0 {
> > >                     /*
> > >                      * As defined in the IEEE Std 1275-1994 document,
> > >                      * reg is a five-cell address encoded as (phys.hi
> > >                      * phys.mid phys.lo size.hi size.lo). phys.hi
> > >                      * should contain the device's BDF as 0b00000000
> > >                      * bbbbbbbb dddddfff 00000000. The other cells
> > >                      * should be zero.
> > >                      */
> > >                     reg = <0 0 0 0 0>;
> > >             };
> > >     };
> > >
> > > The bus is clearly 0. So fix it.
> >
> > s/bus/device/
> >
> > The unit-address format is '<device>,<function>' (and function is
> > optional). The bus number is not part of the unit-address because that
> > is dynamic and then the path would not be fixed/known. The bus is part
> > of 'reg' for true OpenFirmware, but for FDT I think it should always be
> > 0 as the DT is static.
> >
> > Looks like the child node is wrong (both unit-address and reg) as well:
> >
> >                 usb@1,0 {
> >                         reg = <0x10000 0 0 0 0>;
> >                         resets = <&reset RASPBERRYPI_FIRMWARE_RESET_ID_USB>;
> >                 };
> >
> > It doesn't warn because the bridge node is also missing 'device_type =
> > "pci";'.
> >
> > This is all fairly hard to get right (see recent hikey970 patches for a
> > complex example). I'm thinking about writing a tool that generates a DT
> > with PCI nodes by reading the PCI hierachy from sysfs.
>
> Just to double-check I understood everything, with:
>
>         lspci -D -PP
>         0000:00:00.0 PCI bridge: Broadcom Inc. and subsidiaries BCM2711 PCIe Bridge (rev 10)
>         0000:00:00.0/01:00.0 USB controller: VIA Technologies, Inc. VL805/806 xHCI USB 3.0 Controller (rev 01)
>
> It should look like this:
>
>         &pcie0 {
>                 pci@0,0 {
>                         device_type = "pci";
>                         #address-cells = <3>;
>                         #size-cells = <2>;
>                         ranges;
>
>                         reg = <0 0 0 0 0>;
>
>                         usb@0,0 {
>                                 reg = <0 0 0 0 0>;
>                                 resets = <&reset RASPBERRYPI_FIRMWARE_RESET_ID_USB>;
>                         };
>                 };
>         };

Yes, that looks correct.

Rob