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.
> 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@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/7a1e2ebc-f7d8-8431-d844-41a9c36a8911@xxxxxxx
> Signed-off-by: Punit Agrawal <punitagrawal@xxxxxxxxx>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> ---
> 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
>
