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: <CAL_Jsq+m6CkGj_NYGvwxoKwoQ4PkEu6hfGdMTT3i4APoHSkNeg@mail.gmail.com>
Date:   Mon, 19 Apr 2021 10:44:31 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Leonardo Bras <leobras.c@...il.com>
Cc:     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 Fri, Apr 16, 2021 at 3:58 PM Leonardo Bras <leobras.c@...il.com> wrote:
>
> Hello Rob, thanks for this feedback!
>
> On Thu, 2021-04-15 at 13:59 -0500, Rob Herring wrote:
> > +PPC and PCI lists
> >
> > 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.
> >
> > Many others? Looks like sparc and powerpc to me.
> >
>
> s390 also does that, but it look like it comes from a device-tree.

I'm only looking at DT based platforms, and s390 doesn't use DT.

> > 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.
>
> In powerpc I reach this function with this stack, while configuring a
> virtio-net device for a qemu/KVM pseries guest:
>
> pci_process_bridge_OF_ranges+0xac/0x2d4
> pSeries_discover_phbs+0xc4/0x158
> discover_phbs+0x40/0x60
> do_one_initcall+0x60/0x2d0
> kernel_init_freeable+0x308/0x3a8
> kernel_init+0x2c/0x168
> ret_from_kernel_thread+0x5c/0x70
>
> For this, both MMIO32 and MMIO64 resources will have flags 0x200.

Oh good, powerpc has 2 possible flags parsing functions. So in the
above path, do we need to set PCI_BASE_ADDRESS_MEM_TYPE_64?

Does pci_parse_of_flags() get called in your case?

> > 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.
> >
>
> I am not sure if you mean here:
> a) it's ok to add IORESOURCE_MEM_64 here, because it does not affect
> anything else, or
> b) it should be using PCI_BASE_ADDRESS_MEM_TYPE_64
> (or IORESOURCE_MEM_64 | PCI_BASE_ADDRESS_MEM_TYPE_64) instead, since
> it's how it's added in powerpc/sparc, and else there is no point.

I'm wondering if a) is incomplete and PCI_BASE_ADDRESS_MEM_TYPE_64
also needs to be set. The question is ultimately are BARs getting set
correctly for 64-bit? It looks to me like they aren't.

Rob