[PATCH 2/2] PCI: quirks: Drop unassignable 32 GiB BAR 4 on Tenstorrent Blackhole
From: Anirudh Srinivasan
Date: Mon Aug 24 2026 - 13:04:22 EST
Tenstorrent Blackhole cards expose a 32 GiB BAR 4 that is unused by most
software talking to the card. This BAR cannot be assigned on hosts whose
PCI aperture is smaller than 32 GiB (e.g some ARM/RISC-V systems). This
failure also results in BAR 0 (256 MiB) and 2 (2 MiB) being unassigned
because bridge windows are sized as the sum of all enabled child BARs.
This makes the card completely unusable on such systems.
spacemit-k1-pcie 80000000.pcie: PCI host bridge to bus 0000:00
pci_bus 0000:00: root bus resource [bus 00-ff]
pci_bus 0000:00: root bus resource [io 0x100000-0x1fffff] (bus address [0x10000-0x10ffff])
pci_bus 0000:00: root bus resource [mem 0x1100110000-0x117fffffff] (bus address [0x00110000-0x7fffffff])
pci_bus 0000:00: root bus resource [mem 0x1800000000-0x18ffffffff pref]
<snip>
pci 0000:01:00.0: [1e52:b140] type 00 class 0x120000 PCIe Endpoint
pci 0000:01:00.0: BAR 0 [mem 0x00000000-0x1fffffff 64bit pref]
pci 0000:01:00.0: BAR 2 [mem 0x1120000000-0x11200fffff 64bit pref]
pci 0000:01:00.0: BAR 4 [mem 0xfffffff800000000-0xffffffffffffffff 64bit pref]
<snip>
pci 0000:00:00.0: bridge window [mem size 0x820100000 64bit pref]: can't assign; no space
pci 0000:00:00.0: bridge window [mem size 0x820100000 64bit pref]: failed to assign
pci 0000:00:00.0: BAR 0 [mem 0x1108000000-0x110fffffff]: assigned
pci 0000:00:00.0: BAR 1 [mem 0x1110000000-0x1117ffffff]: assigned
pci 0000:00:00.0: BAR 0 [mem 0x1108000000-0x110fffffff]: releasing
pci 0000:00:00.0: BAR 1 [mem 0x1110000000-0x1117ffffff]: releasing
pci 0000:00:00.0: bridge window [mem size 0x820100000 64bit pref]: can't assign; no space
pci 0000:00:00.0: bridge window [mem size 0x820100000 64bit pref]: failed to assign
pci 0000:00:00.0: BAR 0 [mem 0x1108000000-0x110fffffff]: assigned
pci 0000:00:00.0: BAR 1 [mem 0x1110000000-0x1117ffffff]: assigned
pci 0000:01:00.0: BAR 4 [mem size 0x800000000 64bit pref]: can't assign; no space
pci 0000:01:00.0: BAR 4 [mem size 0x800000000 64bit pref]: failed to assign
pci 0000:01:00.0: BAR 0 [mem size 0x20000000 64bit pref]: can't assign; no space
pci 0000:01:00.0: BAR 0 [mem size 0x20000000 64bit pref]: failed to assign
pci 0000:01:00.0: BAR 2 [mem size 0x00100000 64bit pref]: can't assign; no space
pci 0000:01:00.0: BAR 2 [mem size 0x00100000 64bit pref]: failed to assign
pci 0000:01:00.0: BAR 4 [mem size 0x800000000 64bit pref]: can't assign; no space
pci 0000:01:00.0: BAR 4 [mem size 0x800000000 64bit pref]: failed to assign
pci 0000:01:00.0: BAR 0 [mem size 0x20000000 64bit pref]: can't assign; no space
pci 0000:01:00.0: BAR 0 [mem size 0x20000000 64bit pref]: failed to assign
pci 0000:01:00.0: BAR 2 [mem size 0x00100000 64bit pref]: can't assign; no space
pci 0000:01:00.0: BAR 2 [mem size 0x00100000 64bit pref]: failed to assign
Add a header fixup that walks the root-bus apertures and drops BAR 4
when it is larger than every root-bus aperture. Resource assignment
skips resources with zero flags (pdev_resource_assignable()), so the
bridge window then sizes to BARs 0/2 and succeeds. This was tested on a
Spacemit-K3 RISC-V board that has only 4GiB of BAR space. tt-smi and
tt-bh-linux are able to run on the card.
Signed-off-by: Anirudh Srinivasan <asrinivasan@xxxxxxxxxxxxxxxxxxx>
---
drivers/pci/quirks.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index b09f27f7846fc..df54e379c116b 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -6415,3 +6415,35 @@ static void pci_mask_replay_timer_timeout(struct pci_dev *pdev)
DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_GLI, 0x9750, pci_mask_replay_timer_timeout);
DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_GLI, 0x9755, pci_mask_replay_timer_timeout);
#endif
+
+/*
+ * Drop unused 32 GiB BAR 4 on Tenstorrent Blackhole cards so the card is
+ * usable on systems with smaller host bridge apertures.
+ */
+static void quirk_tenstorrent_blackhole_bar4(struct pci_dev *pdev)
+{
+ struct resource *res = &pdev->resource[4];
+ struct pci_bus *bus = pdev->bus;
+ struct resource *win;
+
+ if (!(res->flags & IORESOURCE_MEM))
+ return;
+
+ /* Find the root bus; its resource list holds the host apertures */
+ while (bus->parent)
+ bus = bus->parent;
+
+ pci_bus_for_each_resource(bus, win) {
+ if (!win || !(win->flags & IORESOURCE_MEM))
+ continue;
+ if (resource_size(res) <= resource_size(win))
+ return;
+ }
+
+ pci_info(pdev, "BAR 4 %pR larger than every host bridge aperture, dropping it\n",
+ res);
+ res->start = 0;
+ res->end = 0;
+ res->flags = 0;
+}
+DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_TENSTORRENT, 0xb140, quirk_tenstorrent_blackhole_bar4);
--
2.43.0