The refactoring in upstream commit 4292a1e45fd4 ("PCI: Refactor
distributing available memory to use loops") switched
pci_bus_distribute_available_resources to operate on an array of bridge
windows. That rewrite accidentally looked up bus resources via
pci_bus_resource_n and then passed those pointers to helper routines
that expect the resource to belong to the device. As soon as we
execute that code, pci_resource_num warned because the resource
wasn't in the bridge's resource array.

This happens on my AMD Strix Halo machine with Thunderbolt device, the
error message is shown below:

[    4.212389] ------------[ cut here ]------------
[    4.212391] WARNING: CPU: 6 PID: 272 at drivers/pci/pci.h:471 pci_bus_distribute_available_resources+0x6ad/0x6d0
[    4.212400] Modules linked in: raid6_pq(+) hid_generic uas usb_storage scsi_mod usbhid hid scsi_common amdgpu amdxcp drm_panel_backlight_quirks gpu_sched drm_buddy drm_ttm_helper ttm drm_exec i2c_algo_bit drm_suballoc_helper drm_display_helper cec rc_core drm_client_lib drm_kms_helper sdhci_pci sdhci_uhs2 xhci_pci sp5100_tco xhci_hcd r8169 drm nvme sdhci watchdog realtek usbcore thunderbolt cqhci atlantic nvme_core mdio_devres psmouse libphy mmc_core nvme_keyring video i2c_piix4 macsec nvme_auth serio_raw mdio_bus i2c_smbus usb_common crc16 hkdf wmi
[    4.212443] CPU: 6 UID: 0 PID: 272 Comm: irq/33-pciehp Not tainted 6.17.0+ #1 PREEMPT(voluntary)
[    4.212447] Hardware name: PELADN YO Series/YO1, BIOS 1.04 05/15/2025
[    4.212449] RIP: 0010:pci_bus_distribute_available_resources+0x6ad/0x6d0
[    4.212453] Code: ff e9 a2 48 c7 c7 b8 b7 83 a3 4c 89 4c 24 18 e8 a9 2a fb ff 4c 8b 4c 24 18 e9 ca fd ff ff 48 8b 05 60 53 47 01 e9 94 fe ff ff <0f> 0b e9 5d fe ff ff 48 8b 05 55 53 47 01 e9 81 fe ff ff e8 4b 87
[    4.212455] RSP: 0018:ffffaffcc0d4f9a8 EFLAGS: 00010206
[    4.212458] RAX: 00000000000000cd RBX: ffff9721a687f800 RCX: ffff9721a687c828
[    4.212459] RDX: 0000000000000000 RSI: 00000000000000cd RDI: ffff97218bc8a3c0
[    4.212461] RBP: ffff9721a687c828 R08: ffffaffcc0d4f9f8 R09: 0000000000000001
[    4.212462] R10: ffff97218bc8d700 R11: 0000000000000000 R12: ffffaffcc0d4f9f8
[    4.212462] R13: ffffaffcc0d4f9f8 R14: 0000000000000000 R15: ffff97218bc8a000
[    4.212464] FS:  0000000000000000(0000) GS:ffff973ee1ad9000(0000) knlGS:0000000000000000
[    4.212465] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    4.212467] CR2: 00005640b0f29360 CR3: 0000000ccb224000 CR4: 0000000000f50ef0
[    4.212469] PKRU: 55555554
[    4.212470] Call Trace:
[    4.212473]  <TASK>
[    4.212478]  pci_bus_distribute_available_resources+0x590/0x6d0
[    4.212483]  pci_bridge_distribute_available_resources+0x62/0xb0
[    4.212487]  pci_assign_unassigned_bridge_resources+0x65/0x1b0
[    4.212490]  pciehp_configure_device+0x92/0x160
[    4.212495]  pciehp_handle_presence_or_link_change+0x1b5/0x350
[    4.212498]  pciehp_ist+0x147/0x1c0
[    4.212502]  irq_thread_fn+0x20/0x60
[    4.212508]  irq_thread+0x1cc/0x360
[    4.212511]  ? __pfx_irq_thread_fn+0x10/0x10
[    4.212515]  ? __pfx_irq_thread_dtor+0x10/0x10
[    4.212518]  ? __pfx_irq_thread+0x10/0x10
[    4.212521]  kthread+0xf9/0x240
[    4.212525]  ? __pfx_kthread+0x10/0x10
[    4.212528]  ret_from_fork+0x195/0x1d0
[    4.212533]  ? __pfx_kthread+0x10/0x10
[    4.212536]  ret_from_fork_asm+0x1a/0x30
[    4.212540]  </TASK>
[    4.212541] ---[ end trace 0000000000000000 ]---

Fix the regression by always fetching the resource directly from the
bridge: use pci_resource_n(bridge, PCI_BRIDGE_RESOURCES + i). This
restores the original behaviour while keeping the refactored structure.
And then we can successfully assign resources to the Thunderbolt device.

Fixes: 4292a1e45fd4 ("PCI: Refactor distributing available memory to use loops")

Signed-off-by: Yangyu Chen <cyy@cyyself.name>
---
 drivers/pci/setup-bus.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 362ad108794d..4a8735b275e4 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -2085,7 +2085,8 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
 	int i;
 
 	for (i = 0; i < PCI_P2P_BRIDGE_RESOURCE_NUM; i++) {
-		struct resource *res = pci_bus_resource_n(bus, i);
+		struct resource *res =
+			pci_resource_n(bridge, PCI_BRIDGE_RESOURCES + i);
 
 		available[i] = available_in[i];
 
@@ -2158,7 +2159,7 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
 			continue;
 
 		for (i = 0; i < PCI_P2P_BRIDGE_RESOURCE_NUM; i++) {
-			res = pci_bus_resource_n(bus, i);
+			res = pci_resource_n(dev, PCI_BRIDGE_RESOURCES + i);
 
 			/*
 			 * Make sure the split resource space is properly
-- 
2.51.0

On Wed, Oct 08, 2025 at 10:36:52PM +0800, Yangyu Chen wrote:
> The refactoring in upstream commit 4292a1e45fd4 ("PCI: Refactor
> distributing available memory to use loops") switched
> pci_bus_distribute_available_resources to operate on an array of bridge
> windows. That rewrite accidentally looked up bus resources via
> pci_bus_resource_n and then passed those pointers to helper routines
> that expect the resource to belong to the device. As soon as we
> execute that code, pci_resource_num warned because the resource
> wasn't in the bridge's resource array.
> 
> This happens on my AMD Strix Halo machine with Thunderbolt device, the
> error message is shown below:
> 
> [    4.212389] ------------[ cut here ]------------
> [    4.212391] WARNING: CPU: 6 PID: 272 at drivers/pci/pci.h:471 pci_bus_distribute_available_resources+0x6ad/0x6d0
> [    4.212400] Modules linked in: raid6_pq(+) hid_generic uas usb_storage scsi_mod usbhid hid scsi_common amdgpu amdxcp drm_panel_backlight_quirks gpu_sched drm_buddy drm_ttm_helper ttm drm_exec i2c_algo_bit drm_suballoc_helper drm_display_helper cec rc_core drm_client_lib drm_kms_helper sdhci_pci sdhci_uhs2 xhci_pci sp5100_tco xhci_hcd r8169 drm nvme sdhci watchdog realtek usbcore thunderbolt cqhci atlantic nvme_core mdio_devres psmouse libphy mmc_core nvme_keyring video i2c_piix4 macsec nvme_auth serio_raw mdio_bus i2c_smbus usb_common crc16 hkdf wmi
> [    4.212443] CPU: 6 UID: 0 PID: 272 Comm: irq/33-pciehp Not tainted 6.17.0+ #1 PREEMPT(voluntary)
> [    4.212447] Hardware name: PELADN YO Series/YO1, BIOS 1.04 05/15/2025
> [    4.212449] RIP: 0010:pci_bus_distribute_available_resources+0x6ad/0x6d0
> [    4.212453] Code: ff e9 a2 48 c7 c7 b8 b7 83 a3 4c 89 4c 24 18 e8 a9 2a fb ff 4c 8b 4c 24 18 e9 ca fd ff ff 48 8b 05 60 53 47 01 e9 94 fe ff ff <0f> 0b e9 5d fe ff ff 48 8b 05 55 53 47 01 e9 81 fe ff ff e8 4b 87
> [    4.212455] RSP: 0018:ffffaffcc0d4f9a8 EFLAGS: 00010206
> [    4.212458] RAX: 00000000000000cd RBX: ffff9721a687f800 RCX: ffff9721a687c828
> [    4.212459] RDX: 0000000000000000 RSI: 00000000000000cd RDI: ffff97218bc8a3c0
> [    4.212461] RBP: ffff9721a687c828 R08: ffffaffcc0d4f9f8 R09: 0000000000000001
> [    4.212462] R10: ffff97218bc8d700 R11: 0000000000000000 R12: ffffaffcc0d4f9f8
> [    4.212462] R13: ffffaffcc0d4f9f8 R14: 0000000000000000 R15: ffff97218bc8a000
> [    4.212464] FS:  0000000000000000(0000) GS:ffff973ee1ad9000(0000) knlGS:0000000000000000
> [    4.212465] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    4.212467] CR2: 00005640b0f29360 CR3: 0000000ccb224000 CR4: 0000000000f50ef0
> [    4.212469] PKRU: 55555554
> [    4.212470] Call Trace:
> [    4.212473]  <TASK>
> [    4.212478]  pci_bus_distribute_available_resources+0x590/0x6d0
> [    4.212483]  pci_bridge_distribute_available_resources+0x62/0xb0
> [    4.212487]  pci_assign_unassigned_bridge_resources+0x65/0x1b0
> [    4.212490]  pciehp_configure_device+0x92/0x160
> [    4.212495]  pciehp_handle_presence_or_link_change+0x1b5/0x350
> [    4.212498]  pciehp_ist+0x147/0x1c0
> [    4.212502]  irq_thread_fn+0x20/0x60
> [    4.212508]  irq_thread+0x1cc/0x360
> [    4.212511]  ? __pfx_irq_thread_fn+0x10/0x10
> [    4.212515]  ? __pfx_irq_thread_dtor+0x10/0x10
> [    4.212518]  ? __pfx_irq_thread+0x10/0x10
> [    4.212521]  kthread+0xf9/0x240
> [    4.212525]  ? __pfx_kthread+0x10/0x10
> [    4.212528]  ret_from_fork+0x195/0x1d0
> [    4.212533]  ? __pfx_kthread+0x10/0x10
> [    4.212536]  ret_from_fork_asm+0x1a/0x30
> [    4.212540]  </TASK>
> [    4.212541] ---[ end trace 0000000000000000 ]---
> 
> Fix the regression by always fetching the resource directly from the
> bridge: use pci_resource_n(bridge, PCI_BRIDGE_RESOURCES + i). This
> restores the original behaviour while keeping the refactored structure.
> And then we can successfully assign resources to the Thunderbolt device.
> 
> Fixes: 4292a1e45fd4 ("PCI: Refactor distributing available memory to use loops")
> 
> Signed-off-by: Yangyu Chen <cyy@cyyself.name>

Tentatively applied to pci/for-linus for v6.18, pending Ilpo's review.

Thank you very much for debugging and providing a patch!

> ---
>  drivers/pci/setup-bus.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index 362ad108794d..4a8735b275e4 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -2085,7 +2085,8 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
>  	int i;
>  
>  	for (i = 0; i < PCI_P2P_BRIDGE_RESOURCE_NUM; i++) {
> -		struct resource *res = pci_bus_resource_n(bus, i);
> +		struct resource *res =
> +			pci_resource_n(bridge, PCI_BRIDGE_RESOURCES + i);
>  
>  		available[i] = available_in[i];
>  
> @@ -2158,7 +2159,7 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
>  			continue;
>  
>  		for (i = 0; i < PCI_P2P_BRIDGE_RESOURCE_NUM; i++) {
> -			res = pci_bus_resource_n(bus, i);
> +			res = pci_resource_n(dev, PCI_BRIDGE_RESOURCES + i);
>  
>  			/*
>  			 * Make sure the split resource space is properly
> -- 
> 2.51.0
>

On Wed, 8 Oct 2025, Bjorn Helgaas wrote:
> On Wed, Oct 08, 2025 at 10:36:52PM +0800, Yangyu Chen wrote:
> > The refactoring in upstream commit 4292a1e45fd4 ("PCI: Refactor
> > distributing available memory to use loops") switched
> > pci_bus_distribute_available_resources to operate on an array of bridge
> > windows. That rewrite accidentally looked up bus resources via
> > pci_bus_resource_n and then passed those pointers to helper routines
> > that expect the resource to belong to the device. As soon as we
> > execute that code, pci_resource_num warned because the resource
> > wasn't in the bridge's resource array.
> > 
> > This happens on my AMD Strix Halo machine with Thunderbolt device, the
> > error message is shown below:
> > 
> > [    4.212389] ------------[ cut here ]------------
> > [    4.212391] WARNING: CPU: 6 PID: 272 at drivers/pci/pci.h:471 pci_bus_distribute_available_resources+0x6ad/0x6d0
> > [    4.212400] Modules linked in: raid6_pq(+) hid_generic uas usb_storage scsi_mod usbhid hid scsi_common amdgpu amdxcp drm_panel_backlight_quirks gpu_sched drm_buddy drm_ttm_helper ttm drm_exec i2c_algo_bit drm_suballoc_helper drm_display_helper cec rc_core drm_client_lib drm_kms_helper sdhci_pci sdhci_uhs2 xhci_pci sp5100_tco xhci_hcd r8169 drm nvme sdhci watchdog realtek usbcore thunderbolt cqhci atlantic nvme_core mdio_devres psmouse libphy mmc_core nvme_keyring video i2c_piix4 macsec nvme_auth serio_raw mdio_bus i2c_smbus usb_common crc16 hkdf wmi
> > [    4.212443] CPU: 6 UID: 0 PID: 272 Comm: irq/33-pciehp Not tainted 6.17.0+ #1 PREEMPT(voluntary)
> > [    4.212447] Hardware name: PELADN YO Series/YO1, BIOS 1.04 05/15/2025
> > [    4.212449] RIP: 0010:pci_bus_distribute_available_resources+0x6ad/0x6d0
> > [    4.212453] Code: ff e9 a2 48 c7 c7 b8 b7 83 a3 4c 89 4c 24 18 e8 a9 2a fb ff 4c 8b 4c 24 18 e9 ca fd ff ff 48 8b 05 60 53 47 01 e9 94 fe ff ff <0f> 0b e9 5d fe ff ff 48 8b 05 55 53 47 01 e9 81 fe ff ff e8 4b 87
> > [    4.212455] RSP: 0018:ffffaffcc0d4f9a8 EFLAGS: 00010206
> > [    4.212458] RAX: 00000000000000cd RBX: ffff9721a687f800 RCX: ffff9721a687c828
> > [    4.212459] RDX: 0000000000000000 RSI: 00000000000000cd RDI: ffff97218bc8a3c0
> > [    4.212461] RBP: ffff9721a687c828 R08: ffffaffcc0d4f9f8 R09: 0000000000000001
> > [    4.212462] R10: ffff97218bc8d700 R11: 0000000000000000 R12: ffffaffcc0d4f9f8
> > [    4.212462] R13: ffffaffcc0d4f9f8 R14: 0000000000000000 R15: ffff97218bc8a000
> > [    4.212464] FS:  0000000000000000(0000) GS:ffff973ee1ad9000(0000) knlGS:0000000000000000
> > [    4.212465] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [    4.212467] CR2: 00005640b0f29360 CR3: 0000000ccb224000 CR4: 0000000000f50ef0
> > [    4.212469] PKRU: 55555554
> > [    4.212470] Call Trace:
> > [    4.212473]  <TASK>
> > [    4.212478]  pci_bus_distribute_available_resources+0x590/0x6d0
> > [    4.212483]  pci_bridge_distribute_available_resources+0x62/0xb0
> > [    4.212487]  pci_assign_unassigned_bridge_resources+0x65/0x1b0
> > [    4.212490]  pciehp_configure_device+0x92/0x160
> > [    4.212495]  pciehp_handle_presence_or_link_change+0x1b5/0x350
> > [    4.212498]  pciehp_ist+0x147/0x1c0
> > [    4.212502]  irq_thread_fn+0x20/0x60
> > [    4.212508]  irq_thread+0x1cc/0x360
> > [    4.212511]  ? __pfx_irq_thread_fn+0x10/0x10
> > [    4.212515]  ? __pfx_irq_thread_dtor+0x10/0x10
> > [    4.212518]  ? __pfx_irq_thread+0x10/0x10
> > [    4.212521]  kthread+0xf9/0x240
> > [    4.212525]  ? __pfx_kthread+0x10/0x10
> > [    4.212528]  ret_from_fork+0x195/0x1d0
> > [    4.212533]  ? __pfx_kthread+0x10/0x10
> > [    4.212536]  ret_from_fork_asm+0x1a/0x30
> > [    4.212540]  </TASK>
> > [    4.212541] ---[ end trace 0000000000000000 ]---
> > 
> > Fix the regression by always fetching the resource directly from the
> > bridge: use pci_resource_n(bridge, PCI_BRIDGE_RESOURCES + i). This
> > restores the original behaviour while keeping the refactored structure.
> > And then we can successfully assign resources to the Thunderbolt device.
> > 
> > Fixes: 4292a1e45fd4 ("PCI: Refactor distributing available memory to use loops")
> > 
> > Signed-off-by: Yangyu Chen <cyy@cyyself.name>
> 
> Tentatively applied to pci/for-linus for v6.18, pending Ilpo's review.

Thanks to Yangyu for the patch. 

I see it already was pulled by Linus. No big objection to this as it 
clearly seems to help and should cause no issue to move back to use 
pci_resource_n().

However, that change to pci_bus_resource_n() was very much done 
intentionally as those two calls should have been equivalent. Initially
I was perplexed how this change can fix anything but it seem one of my 
pci_bus_resource_n() conversions was wrong...

> Thank you very much for debugging and providing a patch!
> 
> > ---
> >  drivers/pci/setup-bus.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> > index 362ad108794d..4a8735b275e4 100644
> > --- a/drivers/pci/setup-bus.c
> > +++ b/drivers/pci/setup-bus.c
> > @@ -2085,7 +2085,8 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
> >  	int i;
> >  
> >  	for (i = 0; i < PCI_P2P_BRIDGE_RESOURCE_NUM; i++) {
> > -		struct resource *res = pci_bus_resource_n(bus, i);
> > +		struct resource *res =
> > +			pci_resource_n(bridge, PCI_BRIDGE_RESOURCES + i);

Was this change actually necessary to fix anything or was it changed just 
due to noticing the other case?

> >  
> >  		available[i] = available_in[i];
> >  
> > @@ -2158,7 +2159,7 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
> >  			continue;
> >  
> >  		for (i = 0; i < PCI_P2P_BRIDGE_RESOURCE_NUM; i++) {
> > -			res = pci_bus_resource_n(bus, i);
> > +			res = pci_resource_n(dev, PCI_BRIDGE_RESOURCES + i);

This was misconverted by me, as dev is not same as bridge here, so it 
should have been pci_bus_resource_n(b, i); (b is dev->subordinate).

-- 
 i.

> On 9 Oct 2025, at 20:02, Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> wrote:
> 
> On Wed, 8 Oct 2025, Bjorn Helgaas wrote:
>> On Wed, Oct 08, 2025 at 10:36:52PM +0800, Yangyu Chen wrote:
>>> The refactoring in upstream commit 4292a1e45fd4 ("PCI: Refactor
>>> distributing available memory to use loops") switched
>>> pci_bus_distribute_available_resources to operate on an array of bridge
>>> windows. That rewrite accidentally looked up bus resources via
>>> pci_bus_resource_n and then passed those pointers to helper routines
>>> that expect the resource to belong to the device. As soon as we
>>> execute that code, pci_resource_num warned because the resource
>>> wasn't in the bridge's resource array.
>>> 
>>> This happens on my AMD Strix Halo machine with Thunderbolt device, the
>>> error message is shown below:
>>> 
>>> [    4.212389] ------------[ cut here ]------------
>>> [    4.212391] WARNING: CPU: 6 PID: 272 at drivers/pci/pci.h:471 pci_bus_distribute_available_resources+0x6ad/0x6d0
>>> [    4.212400] Modules linked in: raid6_pq(+) hid_generic uas usb_storage scsi_mod usbhid hid scsi_common amdgpu amdxcp drm_panel_backlight_quirks gpu_sched drm_buddy drm_ttm_helper ttm drm_exec i2c_algo_bit drm_suballoc_helper drm_display_helper cec rc_core drm_client_lib drm_kms_helper sdhci_pci sdhci_uhs2 xhci_pci sp5100_tco xhci_hcd r8169 drm nvme sdhci watchdog realtek usbcore thunderbolt cqhci atlantic nvme_core mdio_devres psmouse libphy mmc_core nvme_keyring video i2c_piix4 macsec nvme_auth serio_raw mdio_bus i2c_smbus usb_common crc16 hkdf wmi
>>> [    4.212443] CPU: 6 UID: 0 PID: 272 Comm: irq/33-pciehp Not tainted 6.17.0+ #1 PREEMPT(voluntary)
>>> [    4.212447] Hardware name: PELADN YO Series/YO1, BIOS 1.04 05/15/2025
>>> [    4.212449] RIP: 0010:pci_bus_distribute_available_resources+0x6ad/0x6d0
>>> [    4.212453] Code: ff e9 a2 48 c7 c7 b8 b7 83 a3 4c 89 4c 24 18 e8 a9 2a fb ff 4c 8b 4c 24 18 e9 ca fd ff ff 48 8b 05 60 53 47 01 e9 94 fe ff ff <0f> 0b e9 5d fe ff ff 48 8b 05 55 53 47 01 e9 81 fe ff ff e8 4b 87
>>> [    4.212455] RSP: 0018:ffffaffcc0d4f9a8 EFLAGS: 00010206
>>> [    4.212458] RAX: 00000000000000cd RBX: ffff9721a687f800 RCX: ffff9721a687c828
>>> [    4.212459] RDX: 0000000000000000 RSI: 00000000000000cd RDI: ffff97218bc8a3c0
>>> [    4.212461] RBP: ffff9721a687c828 R08: ffffaffcc0d4f9f8 R09: 0000000000000001
>>> [    4.212462] R10: ffff97218bc8d700 R11: 0000000000000000 R12: ffffaffcc0d4f9f8
>>> [    4.212462] R13: ffffaffcc0d4f9f8 R14: 0000000000000000 R15: ffff97218bc8a000
>>> [    4.212464] FS:  0000000000000000(0000) GS:ffff973ee1ad9000(0000) knlGS:0000000000000000
>>> [    4.212465] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> [    4.212467] CR2: 00005640b0f29360 CR3: 0000000ccb224000 CR4: 0000000000f50ef0
>>> [    4.212469] PKRU: 55555554
>>> [    4.212470] Call Trace:
>>> [    4.212473]  <TASK>
>>> [    4.212478]  pci_bus_distribute_available_resources+0x590/0x6d0
>>> [    4.212483]  pci_bridge_distribute_available_resources+0x62/0xb0
>>> [    4.212487]  pci_assign_unassigned_bridge_resources+0x65/0x1b0
>>> [    4.212490]  pciehp_configure_device+0x92/0x160
>>> [    4.212495]  pciehp_handle_presence_or_link_change+0x1b5/0x350
>>> [    4.212498]  pciehp_ist+0x147/0x1c0
>>> [    4.212502]  irq_thread_fn+0x20/0x60
>>> [    4.212508]  irq_thread+0x1cc/0x360
>>> [    4.212511]  ? __pfx_irq_thread_fn+0x10/0x10
>>> [    4.212515]  ? __pfx_irq_thread_dtor+0x10/0x10
>>> [    4.212518]  ? __pfx_irq_thread+0x10/0x10
>>> [    4.212521]  kthread+0xf9/0x240
>>> [    4.212525]  ? __pfx_kthread+0x10/0x10
>>> [    4.212528]  ret_from_fork+0x195/0x1d0
>>> [    4.212533]  ? __pfx_kthread+0x10/0x10
>>> [    4.212536]  ret_from_fork_asm+0x1a/0x30
>>> [    4.212540]  </TASK>
>>> [    4.212541] ---[ end trace 0000000000000000 ]---
>>> 
>>> Fix the regression by always fetching the resource directly from the
>>> bridge: use pci_resource_n(bridge, PCI_BRIDGE_RESOURCES + i). This
>>> restores the original behaviour while keeping the refactored structure.
>>> And then we can successfully assign resources to the Thunderbolt device.
>>> 
>>> Fixes: 4292a1e45fd4 ("PCI: Refactor distributing available memory to use loops")
>>> 
>>> Signed-off-by: Yangyu Chen <cyy@cyyself.name>
>> 
>> Tentatively applied to pci/for-linus for v6.18, pending Ilpo's review.
> 
> Thanks to Yangyu for the patch. 
> 
> I see it already was pulled by Linus. No big objection to this as it 
> clearly seems to help and should cause no issue to move back to use 
> pci_resource_n().
> 
> However, that change to pci_bus_resource_n() was very much done 
> intentionally as those two calls should have been equivalent. Initially
> I was perplexed how this change can fix anything but it seem one of my 
> pci_bus_resource_n() conversions was wrong...
> 
>> Thank you very much for debugging and providing a patch!
>> 
>>> ---
>>> drivers/pci/setup-bus.c | 5 +++--
>>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>> 
>>> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
>>> index 362ad108794d..4a8735b275e4 100644
>>> --- a/drivers/pci/setup-bus.c
>>> +++ b/drivers/pci/setup-bus.c
>>> @@ -2085,7 +2085,8 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
>>> int i;
>>> 
>>> for (i = 0; i < PCI_P2P_BRIDGE_RESOURCE_NUM; i++) {
>>> - struct resource *res = pci_bus_resource_n(bus, i);
>>> + struct resource *res =
>>> + pci_resource_n(bridge, PCI_BRIDGE_RESOURCES + i);
> 
> Was this change actually necessary to fix anything or was it changed just 
> due to noticing the other case?

It was changed just to align with the following code.

> 
>>> 
>>> available[i] = available_in[i];
>>> 
>>> @@ -2158,7 +2159,7 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
>>> continue;
>>> 
>>> for (i = 0; i < PCI_P2P_BRIDGE_RESOURCE_NUM; i++) {
>>> - res = pci_bus_resource_n(bus, i);
>>> + res = pci_resource_n(dev, PCI_BRIDGE_RESOURCES + i);
> 
> This was misconverted by me, as dev is not same as bridge here, so it 
> should have been pci_bus_resource_n(b, i); (b is dev->subordinate).

Indeed.

I didn't figure out why pci_bus_resource_n fails at the time to
submit the patch. But I just chose the most confident way to fix
that since it breaks mainline.

Thanks,
Yangyu Chen

> 
> -- 
> i.