[PATCH v6] PCI: Fix BAR resize for devices on a root bus

[Liz Fong-Jones]

pci_do_resource_release_and_resize() releases the device BARs that
share a bridge window with the BAR being resized, but when the device
sits directly on a root bus (pdev->bus->self == NULL) it then skips
resource assignment entirely and returns success, leaving the BARs it
just released unassigned (IORESOURCE_UNSET).

Skipping pbus_reassign_bridge_resources() is correct in that case --
there is no bridge window to adjust -- but the device BARs still have
to be reassigned. Before the BAR release was consolidated into the PCI
core, this case worked for amdgpu because the driver released the BARs
itself and then called pci_assign_unassigned_bus_resources()
unconditionally after the resize, which assigns unassigned device BARs
also on a root bus. Commit db92e3fef53e ("drm/amdgpu: Remove driver
side BAR release before resize") removed that call, so nothing assigns
the released BARs anymore.

This breaks amdgpu completely on the SolidRun HoneyComb LX2K (NXP
LX2160A, arm64, ACPI), where the GPU endpoint is enumerated directly
on the root bus of its segment (there is no root port device, so
pdev->bus->self is NULL):

  amdgpu 0004:01:00.0: BAR 0 [mem 0xa400000000-0xa40fffffff 64bit pref]: releasing
  amdgpu 0004:01:00.0: BAR 2 [mem 0xa410000000-0xa4101fffff 64bit pref]: releasing
  amdgpu 0004:01:00.0: sw_init of IP block <gmc_v8_0> failed -19
  amdgpu 0004:01:00.0: amdgpu_device_ip_init failed
  amdgpu 0004:01:00.0: Fatal error during GPU init

No error is logged because the resize path reports success; amdgpu
then finds BAR0 IORESOURCE_UNSET and bails out with -ENODEV.

When there is no upstream bridge, call pci_bus_assign_resources() on
the root bus to place the BARs released above, using the same
alignment-sorted algorithm as normal enumeration instead of a manual
per-BAR loop. This also walks the rest of the hierarchy under the
root bus, as pci_assign_unassigned_bus_resources() used to for amdgpu
before commit db92e3fef53e ("drm/amdgpu: Remove driver side BAR
release before resize") removed that call -- the core-side fix that
commit asked for ("such a problem should be fixed inside
pci_resize_resource() instead").

pci_bus_assign_resources() returns void, so failure is detected by
checking whether the released BARs are still assigned afterward; if
not, roll back as in the bridged case. This is stricter than the
bridged path -- it fails on any unplaced resource, not just required
ones -- since a root bus typically has one shared window, and failing
loudly seemed better than leaving something silently unassigned.

The root bus path also had a locking bug that any fix here necessarily
touches: the old "goto out" jumped to up_read(&pci_bus_sem) without a
matching down_read() (as does the "goto restore" taken when
pci_dev_res_add_to_list() fails in the release loop). Take pci_bus_sem
before the BAR release loop so every path through the function holds
it exactly once.

Use pci_upstream_bridge() rather than testing pdev->bus->self
directly. The two are usually equivalent, but pci_upstream_bridge()
is the canonical test -- pci_is_root_bus(), which it's built on,
warns that bus->self == NULL doesn't necessarily mean a root bus
(SR-IOV virtual buses from virtfn_add_bus() are the same).

Fixes: 337b1b566db0 ("PCI: Fix restoring BARs on BAR resize rollback path")
Cc: stable@xxxxxxxxxxxxxxx
Link: https://bugs.launchpad.net/ubuntu/+source/linux-hwe-7.0/+bug/2159596
Suggested-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Suggested-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
Assisted-by: Claude:claude-fable-5 checkpatch
Assisted-by: Claude:claude-sonnet-5
Signed-off-by: Liz Fong-Jones <lizf@xxxxxxxxxxxx>
---

Confirmed against v7.3-rc3: drivers/pci/setup-bus.c is unpatched
there, pci_do_resource_release_and_resize() still returns without
reassigning the released BARs when bus->self is NULL.

Tested on the real root-bus hardware this fixes (SolidRun HoneyComb
LX2K): both a manual resize via the resource0_resize sysfs attribute
(shrink to 256M then back to 4G, forcing the release+reassign path
both directions) and amdgpu's own natural probe-time resize (with the
amdgpu.rebar=0 workaround removed) succeed cleanly -- VRAM and BAR
size match, no "Fatal error during GPU init", full IP block init.

Changes in v6:
- Repost, confirmed still affects v7.3-rc3
- Added real-hardware test confirmation (both a manual sysfs-triggered
  resize and amdgpu's own natural probe-time resize)
- Picked up Reviewed-by from Ilpo
- Link to v5: https://patch.msgid.link/20260908-pci-rebar-root-bus-v5-1-a210f405ea81@xxxxxxxxxxxx

 drivers/pci/setup-bus.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index e8c94aa1d3c12..ed16ef7c26fa7 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -2380,6 +2380,7 @@ int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size
 	struct resource *res = pci_resource_n(pdev, resno);
 	struct pci_dev_resource *dev_res;
 	struct pci_bus *bus = pdev->bus;
+	struct pci_dev *bridge = pci_upstream_bridge(pdev);
 	struct resource *b_win, *r;
 	LIST_HEAD(saved);
 	unsigned int i;
@@ -2397,6 +2398,8 @@ int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size
 	if (ret)
 		return ret;
 
+	down_read(&pci_bus_sem);
+
 	pci_dev_for_each_resource(pdev, r, i) {
 		if (i >= PCI_BRIDGE_RESOURCES)
 			break;
@@ -2415,13 +2418,21 @@ int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size
 
 	pci_resize_resource_set_size(pdev, resno, size);
 
-	if (!bus->self)
-		goto out;
+	if (bridge) {
+		ret = pbus_reassign_bridge_resources(bus, res, &saved);
+		if (ret)
+			goto restore;
+	} else {
+		/* No bridge window to adjust; let the core reassign the bus. */
+		pci_bus_assign_resources(bus);
 
-	down_read(&pci_bus_sem);
-	ret = pbus_reassign_bridge_resources(bus, res, &saved);
-	if (ret)
-		goto restore;
+		list_for_each_entry(dev_res, &saved, list) {
+			if (!resource_assigned(dev_res->res)) {
+				ret = -ENOSPC;
+				goto restore;
+			}
+		}
+	}
 
 out:
 	up_read(&pci_bus_sem);
-- 
2.53.0