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

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Date:   Mon,  7 Jun 2021 20:28:53 +0900
From:   Punit Agrawal <punitagrawal@...il.com>
To:     helgaas@...nel.org, robh+dt@...nel.org
Cc:     Punit Agrawal <punitagrawal@...il.com>,
        linux-rockchip@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, alexandru.elisei@....com, wqu@...e.com,
        robin.murphy@....com, pgwipeout@...il.com, ardb@...nel.org,
        briannorris@...omium.org, shawn.lin@...k-chips.com,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: [PATCH v3 1/4] PCI: of: Clear 64-bit flag for non-prefetchable memory below 4GB

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@...nel.org>
Link: https://lore.kernel.org/r/7a1e2ebc-f7d8-8431-d844-41a9c36a8911@arm.com
Signed-off-by: Punit Agrawal <punitagrawal@...il.com>
Tested-by: Alexandru Elisei <alexandru.elisei@....com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Rob Herring <robh+dt@...nel.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