linux-kernel - Re: [PATCH 1/1] of/pci: Add IORESOURCE_MEM_64 to resource flags for 64-bit memory addresses

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Message-ID: <20210609185012.GA2647526@bjorn-Precision-5520>
Date:   Wed, 9 Jun 2021 13:50:12 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Leonardo Bras <leobras.c@...il.com>,
        Frank Rowand <frowand.list@...il.com>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        PCI <linux-pci@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 1/1] of/pci: Add IORESOURCE_MEM_64 to resource flags for
 64-bit memory addresses

On Thu, Apr 15, 2021 at 01:59:52PM -0500, Rob Herring wrote:
> On Thu, Apr 15, 2021 at 1:01 PM Leonardo Bras <leobras.c@...il.com> wrote:
> >
> > Many other resource flag parsers already add this flag when the input
> > has bits 24 & 25 set, so update this one to do the same.

[Adding this to the thread for archaeological purposes since it didn't
make it to the commit log]

The other resource flag parsers appear to be:

  pci_parse_of_flags(u32 addr0, ...)    # powerpc/kernel/pci_of_scan.c
    unsigned int as = addr0 & OF_PCI_ADDR0_SPACE_MASK;
    if (as == OF_PCI_ADDR0_SPACE_MMIO32 || as == OF_PCI_ADDR0_SPACE_MMIO64)
      flags = IORESOURCE_MEM | PCI_BASE_ADDRESS_SPACE_MEMORY;
      if (as == OF_PCI_ADDR0_SPACE_MMIO64)
        flags |= PCI_BASE_ADDRESS_MEM_TYPE_64 | IORESOURCE_MEM_64;

  pci_parse_of_flags(u32 addr0)         # sparc/kernel/pci.c
    if (addr0 & 0x02000000) {
      flags = IORESOURCE_MEM | PCI_BASE_ADDRESS_SPACE_MEMORY;
      if (addr0 & 0x01000000)
        flags |= IORESOURCE_MEM_64 | PCI_BASE_ADDRESS_MEM_TYPE_64;

  of_bus_pci_get_flags(... addr)        # drivers/of/address.c (this one)
    u32 w = be32_to_cpup(addr);
    switch((w >> 24) & 0x03) {
    case 0x02: /* 32 bits */
      flags |= IORESOURCE_MEM;
      break;
    case 0x03: /* 64 bits */
      flags |= IORESOURCE_MEM | IORESOURCE_MEM_64;
      break;

It's super annoying to have three copies of essentially the same
thing.  Even more annoying that they test the same things in three
completely different ways.  But I remember looking at this several
years ago, and it wasn't as simple to unify these as I had hoped.

> Many others? Looks like sparc and powerpc to me. Those would be the
> ones I worry about breaking. Sparc doesn't use of/address.c so it's
> fine. Powerpc version of the flags code was only fixed in 2019, so I
> don't think powerpc will care either.

I'm guessing you're referring to df5be5be8735 ("powerpc/pci/of: Fix OF
flags parsing for 64bit BARs").

> I noticed both sparc and powerpc set PCI_BASE_ADDRESS_MEM_TYPE_64 in
> the flags. AFAICT, that's not set anywhere outside of arch code. So
> never for riscv, arm and arm64 at least. That leads me to
> pci_std_update_resource() which is where the PCI code sets BARs and
> just copies the flags in PCI_BASE_ADDRESS_MEM_MASK ignoring
> IORESOURCE_* flags. So it seems like 64-bit is still not handled and
> neither is prefetch.
> 
> > Some devices (like virtio-net) have more than one memory resource
> > (like MMIO32 and MMIO64) and without this flag it would be needed to
> > verify the address range to know which one is which.
> >
> > Signed-off-by: Leonardo Bras <leobras.c@...il.com>
> > ---
> >  drivers/of/address.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/of/address.c b/drivers/of/address.c
> > index 73ddf2540f3f..dc7147843783 100644
> > --- a/drivers/of/address.c
> > +++ b/drivers/of/address.c
> > @@ -116,9 +116,12 @@ static unsigned int of_bus_pci_get_flags(const __be32 *addr)
> >                 flags |= IORESOURCE_IO;
> >                 break;
> >         case 0x02: /* 32 bits */
> > -       case 0x03: /* 64 bits */
> >                 flags |= IORESOURCE_MEM;
> >                 break;
> > +
> > +       case 0x03: /* 64 bits */
> > +               flags |= IORESOURCE_MEM | IORESOURCE_MEM_64;
> > +               break;
> >         }
> >         if (w & 0x40000000)
> >                 flags |= IORESOURCE_PREFETCH;
> > --
> > 2.30.2
> >