[PATCH v2 3/3] PCI: Skip bridge window reads when window is not supported

[Caleb James DeLisle <cjd@cjdns.fr>]

pci_read_bridge_io() and pci_read_bridge_mmio_pref() read bridge window
registers unconditionally. If the registers are hardwired to zero
(not implemented), both base and limit will be 0. Since (0 <= 0) is
true, a bogus window [mem 0x00000000-0x000fffff] or [io 0x0000-0x0fff]
gets created.

pci_read_bridge_windows() already detects unsupported windows by
testing register writability and sets io_window/pref_window flags
accordingly. Check these flags at the start of pci_read_bridge_io()
and pci_read_bridge_mmio_pref() to skip reading registers when the
window is not supported.

Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
Link: https://lore.kernel.org/all/20260113210259.GA715789@bhelgaas/
Signed-off-by: Ahmed Naseef <naseefkm@gmail.com>
Signed-off-by: Caleb James DeLisle <cjd@cjdns.fr>
---
 drivers/pci/probe.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index bccc7a4bdd79..4eacb741b4ec 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -395,6 +395,9 @@ static void pci_read_bridge_io(struct pci_dev *dev, struct resource *res,
 	unsigned long io_mask, io_granularity, base, limit;
 	struct pci_bus_region region;
 
+	if (!dev->io_window)
+		return;
+
 	io_mask = PCI_IO_RANGE_MASK;
 	io_granularity = 0x1000;
 	if (dev->io_window_1k) {
@@ -465,6 +468,9 @@ static void pci_read_bridge_mmio_pref(struct pci_dev *dev, struct resource *res,
 	pci_bus_addr_t base, limit;
 	struct pci_bus_region region;
 
+	if (!dev->pref_window)
+		return;
+
 	pci_read_config_word(dev, PCI_PREF_MEMORY_BASE, &mem_base_lo);
 	pci_read_config_word(dev, PCI_PREF_MEMORY_LIMIT, &mem_limit_lo);
 	base64 = (mem_base_lo & PCI_PREF_RANGE_MASK) << 16;
-- 
2.39.5