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

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Message-ID: <YSzfoyesEzAuLkSS@robh.at.kernel.org>
Date:   Mon, 30 Aug 2021 08:39:47 -0500
From:   Rob Herring <robh@...nel.org>
To:     Nicolas Saenz Julienne <nsaenzju@...hat.com>
Cc:     nsaenz@...nel.org, f.fainelli@...il.com,
        gregkh@...uxfoundation.org, devicetree@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        stefan.wahren@...e.com
Subject: Re: [PATCH] ARM: dts: bcm2711-rpi-4-b: Fix pcie0's unit address

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.

Rob