Re: [PATCH 1/2] PCI: of: Override 64-bit flag for non-prefetchable memory below 4GB
From: Bjorn Helgaas <helgaas@kernel.org>
Date: 2021-05-27 16:21:37
Also in:
linux-pci, linux-rockchip, lkml
On Fri, May 28, 2021 at 12:05:41AM +0900, Punit Agrawal wrote:
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.Conceptually, I'm not sure why we need IORESOURCE_MEM_64 at all on resources we get from DT. I think the main point of IORESOURCE_MEM_64 is to convey the information that "this register, e.g., a PCI BAR, has space for 64-bit values if you need to write to it." When we're parsing this from DT, I think we're just getting a fixed value and there's no concept of writing anything back, so it doesn't seem like we should need to know how wide the hardware register is, or even whether there *is* a hardware register. But I'm sure the PCI resource allocation code probably depends on IORESOURCE_MEM_64 in those host bridge windows in very ugly ways.
quoted hunk ↗ jump to hunk
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@kernel.org> Link: https://lore.kernel.org/r/7a1e2ebc-f7d8-8431-d844-41a9c36a8911@arm.com (local) Signed-off-by: Punit Agrawal <redacted> Cc: Bjorn Helgaas <bhelgaas@google.com> Cc: Rob Herring <robh+dt@kernel.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");
Maybe "Clearing 64-bit flag"?
Can you include %pR, so we see the resource in question?
Unrelated but close by, would be nice if the preceding warning ("size
exceeds max") also included %pR.
+ res->flags &= ~IORESOURCE_MEM_64; + } + } break; } } -- 2.30.2
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