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

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Date:   Fri, 16 Apr 2021 18:27:03 -0300
From:   Leonardo Bras <leobras.c@...il.com>
To:     Rob Herring <robh+dt@...nel.org>
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

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.

> 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.

> 
> 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.

Again, thanks for helping!

Best regards,
Leonardo Bras