On Thu, 6 Jun 2019 at 11:00, Benjamin Herrenschmidt
<benh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
>
> On arm64 ACPI systems, we unconditionally reconfigure the entire PCI
> hierarchy at boot. This is a departure from what is customary on ACPI
> systems, and may break assumptions in some places (e.g., EFIFB), that
> the kernel will leave BARs of enabled PCI devices where they are.
>
> Given that PCI already specifies a device specific ACPI method (_DSM)
> for PCI root bridge nodes that tells us whether the firmware thinks
> the configuration should be left alone, let's sidestep the entire
> policy debate about whether the PCI configuration should be preserved
> or not, and put it under the control of the firmware instead.
>
> [BenH: Added pci_assign_unassigned_root_bus_resources()]
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
>
> So I would like this variant rather than mucking around with
> IORESOURCE_PCI_FIXED at this stage to fix the problem with our platforms.
>
> See my other email, IORESOURCE_PCI_FIXED doesn't really work terribly well
> when using pci_bus_size_bridges and pci_bus_assign_resources, and the
> resulting patches are ugly and add more mess.
>
> Long run, I propose to start working on consolidating all those various
> resource survey mechanisms around what x86 does, unless people strongly
> object... (with the addition of the probe only and force reassign quirks
> so platforms can still chose that).
>
> Note: I haven't tested the effect of pci_assign_unassigned_root_bus_resources
> as our platforms don't leave anything unassigned. I'm not entirely sure how
> well pci_bus_claim_resources() will deal with a partially assigned setup...
>
> We do want to support partial assignment by BIOS though, it's a trend to
> reduce boot time, people seem to want BIOSes to only assign what's critical
> for booting.
>
> Bjorn: I haven't made the claim path the default in absence of _DSM #5 yet.
> I suggest we do that as a separate patch in case it breaks somebody, thus
> making bisection more meaningful. It will also make this one more palatable
> to distros since it won't change the behaviour on systems without _DSM #5,
> and we verified nobody has it except Seattle which returns 1.
>
FYI Seattle is broken in any case since it returns Package(1) rather
than just an int.
The problem with this patch is that currently, the PCI fw spec permits
_DSM #5 everywhere *except* on the host bridge device object itself,
and this is in the process of being changed.
I will leave it up to the maintainers to decide whether we can take
this patch in anticipation of that, even though it doesn't deal with
_DSM #5 on nodes anywhere else in the PCIe tree.
> arch/arm64/kernel/pci.c | 23 +++++++++++++++++++++--
> include/linux/pci-acpi.h | 7 ++++---
> 2 files changed, 25 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> index bb85e2f4603f..6358e1cb4f9f 100644
> --- a/arch/arm64/kernel/pci.c
> +++ b/arch/arm64/kernel/pci.c
> @@ -168,6 +168,7 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
> struct acpi_pci_generic_root_info *ri;
> struct pci_bus *bus, *child;
> struct acpi_pci_root_ops *root_ops;
> + union acpi_object *obj;
>
> ri = kzalloc(sizeof(*ri), GFP_KERNEL);
> if (!ri)
> @@ -193,8 +194,26 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
> if (!bus)
> return NULL;
>
> - pci_bus_size_bridges(bus);
> - pci_bus_assign_resources(bus);
> + /*
> + * Invoke the PCI device specific method (_DSM) #5 'Ignore PCI Boot
> + * Configuration', which tells us whether the firmware wants us to
> + * preserve the configuration of the PCI resource tree for this root
> + * bridge.
> + */
> + obj = acpi_evaluate_dsm(ACPI_HANDLE(bus->bridge), &pci_acpi_dsm_guid, 1,
> + IGNORE_PCI_BOOT_CONFIG_DSM, NULL);
> + if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0) {
> + /* preserve existing resource assignment */
> + pci_bus_claim_resources(bus);
> +
> + /* Assign anything that might have been left out */
> + pci_assign_unassigned_root_bus_resources(bus);
> + } else {
> + /* reconfigure the resource tree from scratch */
> + pci_bus_size_bridges(bus);
> + pci_bus_assign_resources(bus);
> + }
> + ACPI_FREE(obj);
>
> list_for_each_entry(child, &bus->children, node)
> pcie_bus_configure_settings(child);
> diff --git a/include/linux/pci-acpi.h b/include/linux/pci-acpi.h
> index 8082b612f561..62b7fdcc661c 100644
> --- a/include/linux/pci-acpi.h
> +++ b/include/linux/pci-acpi.h
> @@ -107,9 +107,10 @@ static inline void acpiphp_check_host_bridge(struct acpi_device *adev) { }
> #endif
>
> extern const guid_t pci_acpi_dsm_guid;
> -#define DEVICE_LABEL_DSM 0x07
> -#define RESET_DELAY_DSM 0x08
> -#define FUNCTION_DELAY_DSM 0x09
> +#define IGNORE_PCI_BOOT_CONFIG_DSM 0x05
> +#define DEVICE_LABEL_DSM 0x07
> +#define RESET_DELAY_DSM 0x08
> +#define FUNCTION_DELAY_DSM 0x09
>
> #else /* CONFIG_ACPI */
> static inline void acpi_pci_add_bus(struct pci_bus *bus) { }
>
>
