linux-kernel - Re: [PATCH 1/2] PCI: Setup bridge resources earlier

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Message-ID: <017ff8df-511c-4da8-b3cf-edf2cb7f1a67@packett.cool>
Date: Mon, 6 Oct 2025 05:00:25 -0300
From: Val Packett <val@...kett.cool>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
 Krzysztof Wilczyński <kw@...ux.com>,
 "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
 linux-kernel@...r.kernel.org
Cc: Lucas De Marchi <lucas.demarchi@...el.com>
Subject: Re: [PATCH 1/2] PCI: Setup bridge resources earlier

Hi,

On 9/24/25 10:42 AM, Ilpo Järvinen wrote:
> Bridge windows are read twice from PCI Config Space, the first read is
> made from pci_read_bridge_windows() which does not setup the device's
> resources. It causes problems down the road as child resources of the
> bridge cannot check whether they reside within the bridge window or
> not.
>
> Setup the bridge windows already in pci_read_bridge_windows().
>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

Looks like this change has broken the WiFi (but not NVMe) on my 
Snapdragon X1E laptop (Latitude 7455):

qcom-pcie 1c08000.pci: PCI host bridge to bus 0004:00
pci_bus 0004:00: root bus resource [bus 00-ff]
pci_bus 0004:00: root bus resource [io  0x100000-0x1fffff] (bus address 
[0x0000-0xfffff])
pci_bus 0004:00: root bus resource [mem 0x7c300000-0x7dffffff]
pci 0004:00:00.0: [17cb:0111] type 01 class 0x060400 PCIe Root Port
pci 0004:00:00.0: BAR 0 [mem 0x00000000-0x00000fff]
pci 0004:00:00.0: PCI bridge to [bus 01-ff]
pci 0004:00:00.0:   bridge window [io  0x100000-0x100fff]
pci 0004:00:00.0:   bridge window [mem 0x00000000-0x000fffff]
pci 0004:00:00.0:   bridge window [mem 0x00000000-0x000fffff 64bit pref]
pci 0004:00:00.0: PME# supported from D0 D3hot D3cold
pci 0004:00:00.0: bridge window [mem 0x7c300000-0x7c3fffff]: assigned
pci 0004:00:00.0: bridge window [mem 0x7c400000-0x7c4fffff 64bit pref]: 
assigned
pci 0004:00:00.0: BAR 0 [mem 0x7c500000-0x7c500fff]: assigned
pci 0004:00:00.0: bridge window [io  0x100000-0x100fff]: assigned
pci 0004:00:00.0: PCI bridge to [bus 01-ff]
pci 0004:00:00.0:   bridge window [io  0x100000-0x100fff]
pci 0004:00:00.0:   bridge window [mem 0x7c300000-0x7c3fffff]
pci 0004:00:00.0:   bridge window [mem 0x7c400000-0x7c4fffff 64bit pref]
pci_bus 0004:00: resource 4 [io  0x100000-0x1fffff]
pci_bus 0004:00: resource 5 [mem 0x7c300000-0x7dffffff]
pci_bus 0004:01: resource 0 [io  0x100000-0x100fff]
pci_bus 0004:01: resource 1 [mem 0x7c300000-0x7c3fffff]
pci_bus 0004:01: resource 2 [mem 0x7c400000-0x7c4fffff 64bit pref]
pcieport 0004:00:00.0: PME: Signaling with IRQ 186
pcieport 0004:00:00.0: AER: enabled with IRQ 186
pci 0004:01:00.0: [17cb:1107] type 00 class 0x028000 PCIe Endpoint
pci 0004:01:00.0: BAR 0 [mem 0x00000000-0x001fffff 64bit]
pci 0004:01:00.0: PME# supported from D0 D3hot D3cold
pci 0004:01:00.0: BAR 0 [mem size 0x00200000 64bit]: can't assign; no space
pci 0004:01:00.0: BAR 0 [mem size 0x00200000 64bit]: failed to assign
pci 0004:01:00.0: BAR 0 [mem size 0x00200000 64bit]: can't assign; no space
pci 0004:01:00.0: BAR 0 [mem size 0x00200000 64bit]: failed to assign
ath12k_pci 0004:01:00.0: BAR 0 [??? 0x00000000 flags 0x20000000]: can't 
assign; bogus alignment
ath12k_pci 0004:01:00.0: failed to assign pci resource: -22
ath12k_pci 0004:01:00.0: failed to claim device: -22
ath12k_pci 0004:01:00.0: probe with driver ath12k_pci failed with error -22


For comparison, with this change reverted it works again:

qcom-pcie 1c08000.pci: PCI host bridge to bus 0004:00
pci_bus 0004:00: root bus resource [bus 00-ff]
pci_bus 0004:00: root bus resource [io  0x0000-0xfffff]
pci_bus 0004:00: root bus resource [mem 0x7c300000-0x7dffffff]
pci 0004:00:00.0: [17cb:0111] type 01 class 0x060400 PCIe Root Port
pci 0004:00:00.0: BAR 0 [mem 0x00000000-0x00000fff]
pci 0004:00:00.0: PCI bridge to [bus 01-ff]
pci 0004:00:00.0:   bridge window [io  0x0000-0x0fff]
pci 0004:00:00.0:   bridge window [mem 0x00000000-0x000fffff]
pci 0004:00:00.0:   bridge window [mem 0x00000000-0x000fffff 64bit pref]
pci 0004:00:00.0: PME# supported from D0 D3hot D3cold
pci 0004:00:00.0: BAR 0 [mem 0x7c300000-0x7c300fff]: assigned
pci 0004:00:00.0: PCI bridge to [bus 01-ff]
pci_bus 0004:00: resource 4 [io  0x0000-0xfffff]
pci_bus 0004:00: resource 5 [mem 0x7c300000-0x7dffffff]
pcieport 0004:00:00.0: PME: Signaling with IRQ 195
pcieport 0004:00:00.0: AER: enabled with IRQ 195
pci 0004:01:00.0: [17cb:1107] type 00 class 0x028000 PCIe Endpoint
pci 0004:01:00.0: BAR 0 [mem 0x00000000-0x001fffff 64bit]
pci 0004:01:00.0: PME# supported from D0 D3hot D3cold
pci 0004:01:00.0: ASPM: DT platform, enabling L0s-up L0s-dw L1 ASPM-L1.1 
ASPM-L1.2 PCI-PM-L1.1 PCI-PM-L1.2
pci 0004:01:00.0: ASPM: DT platform, enabling ClockPM
pcieport 0004:00:00.0: bridge window [mem 0x7c400000-0x7c5fffff]: assigned
pci 0004:01:00.0: BAR 0 [mem 0x7c400000-0x7c5fffff 64bit]: assigned
ath12k_pci 0004:01:00.0: BAR 0 [mem 0x7c400000-0x7c5fffff 64bit]: assigned
ath12k_pci 0004:01:00.0: enabling device (0000 -> 0002)
ath12k_pci 0004:01:00.0: MSI vectors: 16
ath12k_pci 0004:01:00.0: Hardware name: wcn7850 hw2.0

Not quite sure what's going on with these windows..

~val