linux-kernel - [PATCH 1/2] PCI: of: Override 64-bit flag for non-prefetchable memory below 4GB

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Date:   Fri, 28 May 2021 00:05:41 +0900
From:   Punit Agrawal <punitagrawal@...il.com>
To:     linux-rockchip@...ts.infradead.org, linux-pci@...r.kernel.org
Cc:     Punit Agrawal <punitagrawal@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...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, helgaas@...nel.org, robh+dt@...nel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: [PATCH 1/2] PCI: of: Override 64-bit flag for non-prefetchable memory below 4GB

Some host bridges advertise non-prefetable 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-to-PCI bridges cannot forward 64-bit non-prefetchable memory
ranges. As a result, the change in behaviour due to the commit causes
allocation failure for devices that are connected behind PCI host
bridges modelled as PCI-to-PCI bridge and require non-prefetchable bus
addresses.

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

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>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Rob Herring <robh+dt@...nel.org>
---
 drivers/pci/of.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index da5b414d585a..b9d0bee5a088 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -565,10 +565,14 @@ static int pci_parse_request_of_pci_ranges(struct device *dev,
 		case IORESOURCE_MEM:
 			res_valid |= !(res->flags & IORESOURCE_PREFETCH);

-			if (!(res->flags & IORESOURCE_PREFETCH))
+			if (!(res->flags & IORESOURCE_PREFETCH)) {
 				if (upper_32_bits(resource_size(res)))
 					dev_warn(dev, "Memory resource size exceeds max for 32 bits\n");
-
+				if ((res->flags & IORESOURCE_MEM_64) && !upper_32_bits(res->end)) {
+					dev_warn(dev, "Overriding 64-bit flag for non-prefetchable memory below 4GB\n");
+					res->flags &= ~IORESOURCE_MEM_64;
+				}
+			}
 			break;
 		}
 	}
-- 
2.30.2