[PATCH v3 1/4] PCI: of: Clear 64-bit flag for non-prefetchable memory below 4GB

Punit Agrawal
2021-06-07T11:31:10Z

Some host bridges advertise non-prefetchable memory windows that are
entirely located below 4GB but are marked as 64-bit address memory.

Since commit 9d57e61bf723 ("of/pci: Add IORESOURCE_MEM_64 to resource
flags for 64-bit memory addresses"), the OF PCI range parser takes a
stricter view and treats 64-bit address ranges as advertised while
before such ranges were treated as 32-bit.

A PCI root port modelled as a PCI-to-PCI bridge cannot forward 64-bit
non-prefetchable memory ranges. As a result, the change in behaviour
due to the commit causes failure to allocate 32-bit BAR from a 64-bit
non-prefetchable window.

In order to not break platforms where non-prefetchable memory ranges
lie entirely below 4GB, clear the 64-bit flag.

Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/7a1e2ebc-f7d8-8431-d844-41a9c36a8911@arm.com
Signed-off-by: Punit Agrawal <punitagrawal@gmail.com>
Tested-by: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Rob Herring <robh+dt@kernel.org>
---
drivers/pci/of.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 85dcb7097da4..1e45186a5715 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -353,6 +353,14 @@ static int devm_of_pci_get_host_bridge_resources(struct device *dev,
dev_warn(dev, "More than one I/O resource converted for %pOF. CPU base address for old range lost!\n",
dev_node);
*io_base = range.cpu_addr;
+ } else if (resource_type(res) == IORESOURCE_MEM) {
+ if (!(res->flags & IORESOURCE_PREFETCH)) {
+ if (res->flags & IORESOURCE_MEM_64)
+ if (!upper_32_bits(range.pci_addr + range.size - 1)) {
+ dev_warn(dev, "Clearing 64-bit flag for non-prefetchable memory below 4GB\n");
+ res->flags &= ~IORESOURCE_MEM_64;
+ }
+ }
}

pci_add_resource_offset(resources, res, res->start - range.pci_addr);
--
2.30.2