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Date: Mon, 12 Jun 2017 17:55:25 +0100
From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Bjorn Helgaas <helgaas@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>,
	"linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>,
	linux-pci <linux-pci@vger.kernel.org>,
	Graeme Gregory <graeme.gregory@linaro.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Leif Lindholm <leif.lindholm@linaro.org>,
	Sinan Kaya <okaya@codeaurora.org>, Tomasz Nowicki <tn@semihalf.com>
Subject: Re: [PATCH 0/2] arm64: acpi/pci: allow the firmware BAR
 configuration to be preserved
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On Wed, Jun 07, 2017 at 01:45:19PM +0000, Ard Biesheuvel wrote:
> On 6 June 2017 at 10:02, Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote:
> > On Tue, Jun 06, 2017 at 09:14:26AM +0000, Ard Biesheuvel wrote:
> >
> > [...]
> >
> >> > Do you want me to create a branch out of these patches (inclusive of
> >> > another patch to fix this bus reallocation policy discrepancy) for
> >> > ARM64 folks to test ? Let me know, thanks !
> >> >
> >>
> >> Hi Lorenzo,
> >>
> >> Bjorn has already picked up #1, which is now in -next. I will get back
> >> to this topic today or tomorrow, so let me respin (including the bus
> >> range fix) first, ok?
> >
> > Of course, I just want to help you make progress on this, I think
> > we need help for testing them on ARM64 systems to see how to proceed.
> >
> 
> OK, so I am hitting another issue. While it is quite simple to do this
> 
> """
> diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> index c7e3e6387a49..9a529c6369ac 100644
> --- a/arch/arm64/kernel/pci.c
> +++ b/arch/arm64/kernel/pci.c
> @@ -203,6 +203,9 @@
>                 return NULL;
>         }
> 
> +       /* ignore bus ranges assigned by the firmware */
> +       pci_add_flags(PCI_REASSIGN_ALL_BUS);
> +
>         root_ops->release_info = pci_acpi_generic_release_info;
>         root_ops->prepare_resources = pci_acpi_root_prepare_resources;
>         root_ops->pci_ops = &ri->cfg->ops->pci_ops;
> """
> 
> and get the ACPI code to behave in the same way as the DT code,
> including the resulting quirks, i.e.
> 
> pci_bus 0000:01: busn_res: can not insert [bus 01-ff] under [bus
> 00-0f] (conflicts with (null) [bus 00-0f])
> 
> there are two problems when we want to refine this to take _DSM #5 into account.
> 
> 1) PCI_REASSIGN_ALL_BUS is a global flag, while _DSM is per PCI root
> 2) setting the flag conditionally on whether _DSM #5 allows it is
> difficult to achieve, given that the flag needs to be set before
> acpi_pci_root_create(), at which point we cannot access the _DSM yet

(2) Why ? You have the ACPI root bridge handle at that point. Anyway
(1) makes (2) irrelevant unfortunately.

> So I can send out the above as a separate patch, but right now, I am
> not entirely sure how to proceed with conditionally preserving the
> firmware configuration.

Yes, this definitely requires some focus because that's becoming a bit
unwieldy to manage consistently, I will look into this.

Thanks !
Lorenzo