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

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Message-ID: <CAL_Jsq+Sp_Owe4V4WNh4jnuNJZ5jXxA+j4fW7564oPCy5Lu3ew@mail.gmail.com>
Date:   Thu, 27 May 2021 11:38:46 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Punit Agrawal <punitagrawal@...il.com>
Cc:     "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        PCI <linux-pci@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexandru Elisei <alexandru.elisei@....com>, wqu@...e.com,
        Robin Murphy <robin.murphy@....com>,
        Peter Geis <pgwipeout@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Brian Norris <briannorris@...omium.org>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 1/2] PCI: of: Override 64-bit flag for non-prefetchable
 memory below 4GB

On Thu, May 27, 2021 at 10:06 AM Punit Agrawal <punitagrawal@...il.com> 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.
>
> 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");

Based on Ard's explanation, doesn't this need to also check for
!IORESOURCE_MEM_64?

> -
> +                               if ((res->flags & IORESOURCE_MEM_64) && !upper_32_bits(res->end)) {

res->end is the CPU address space. Isn't it the PCI address space we care about?

> +                                       dev_warn(dev, "Overriding 64-bit flag for non-prefetchable memory below 4GB\n");
> +                                       res->flags &= ~IORESOURCE_MEM_64;
> +                               }
> +                       }
>                         break;
>                 }
>         }
> --
> 2.30.2
>