| Message ID | 20170411163313.18577-3-ard.biesheuvel@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Delegated to: | Bjorn Helgaas |
| Headers | show |
On Tue, Apr 11, 2017 at 05:33:13PM +0100, Ard Biesheuvel wrote: > 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. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > arch/arm64/kernel/pci.c | 20 ++++++++++++++++++-- > include/linux/pci-acpi.h | 7 ++++--- > 2 files changed, 22 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c > index 4f0e3ebfea4b..c88e07e2eb84 100644 > --- a/arch/arm64/kernel/pci.c > +++ b/arch/arm64/kernel/pci.c > @@ -185,6 +185,7 @@ 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_node(sizeof(*ri), GFP_KERNEL, node); > if (!ri) > @@ -208,8 +209,23 @@ 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_uuid, 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); Ok. By the PCI FW specs, we should also assign unassigned resources here (ie resources that can't be claimed). Furthermore, by the PCI FW spec, if !obj this is the path we should be taking (PCI firmware specification Rev 3.1, 4.6.5, Description: 0:) "...This situation is the same as the legacy situation where this _DSM is not provided." which makes me think that the PCI FW specification expects FW set-up to be claimed on boot, it is my interpretation. I wonder how many UEFI developers know this _DSM even exists. If we want to enforce it at least we should mandate its usage at SBSA level, it is a major change and I want to understand the reasons behind it, so far, as I said, I may see why this was needed on x86 but on ARM64 I really don't. Lorenzo > + } 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 7a4e83a8c89c..308111489b83 100644 > --- a/include/linux/pci-acpi.h > +++ b/include/linux/pci-acpi.h > @@ -106,9 +106,10 @@ static inline void acpiphp_check_host_bridge(struct acpi_device *adev) { } > #endif > > extern const u8 pci_acpi_dsm_uuid[]; > -#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) { } > -- > 2.9.3 >
On 4/12/2017 1:26 PM, Lorenzo Pieralisi wrote: >> + if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0) { >> + /* preserve existing resource assignment */ >> + pci_bus_claim_resources(bus); > Ok. By the PCI FW specs, we should also assign unassigned resources here > (ie resources that can't be claimed). Furthermore, by the PCI FW spec, > if !obj this is the path we should be taking (PCI firmware specification > Rev 3.1, 4.6.5, Description: 0:) > > "...This situation is the same as the legacy situation where this > _DSM is not provided." > > which makes me think that the PCI FW specification expects FW set-up > to be claimed on boot, it is my interpretation. > > I wonder how many UEFI developers know this _DSM even exists. If we > want to enforce it at least we should mandate its usage at SBSA level, > it is a major change and I want to understand the reasons behind it, > so far, as I said, I may see why this was needed on x86 but on ARM64 > I really don't. IMO, DSMs are always considered optional to enable additional features in the operating system that otherwise are not required or are not defined in any of the PCI specs. I think we are abusing the DSM here. We want to require the presence of a DSM but we want to require it to be 0 in order to have a UEFI compatible behavior. I think we need to turn it the other way around by having a UEFI compatible behavior and do reassign only if this DSM is 1. I understand that you are worried about regressions. We can try to fix it however time it takes before merging this.
On Wed, Apr 12, 2017 at 02:03:25PM -0400, Sinan Kaya wrote: > On 4/12/2017 1:26 PM, Lorenzo Pieralisi wrote: > >> + if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0) { > >> + /* preserve existing resource assignment */ > >> + pci_bus_claim_resources(bus); > > Ok. By the PCI FW specs, we should also assign unassigned resources here > > (ie resources that can't be claimed). Furthermore, by the PCI FW spec, > > if !obj this is the path we should be taking (PCI firmware specification > > Rev 3.1, 4.6.5, Description: 0:) > > > > "...This situation is the same as the legacy situation where this > > _DSM is not provided." > > > > which makes me think that the PCI FW specification expects FW set-up > > to be claimed on boot, it is my interpretation. I read that section as saying "if the _DSM doesn't exist, or if the _DSM returns 0, the OS must preserve any BAR and bridge window assignments done by firmware." I was not aware of any other statement that restricted the OS from changing assignments done by firmware, and I've always assumed that the OS completely owns PCI devices after handoff from firmware. But maybe my assumption has been wrong. And I know there are BIOSes that do assume the OS doesn't change things, e.g., for the HP iLO, which is used by runtime firmware. The _DSM is generic, not arm64-specific, so if we add support for it, I'd like to at least evaluate the _DSM in the generic code somewhere, e.g., in drivers/pci/pci-acpi.c where we evaluate it for other function indices. Maybe we will still need arch-specific code to use the generic knowledge. Or maybe we should add x86 code to prevent reassignment unless this _DSM returns 1, although that might break some of the "pci=realloc" scenarios. Bjorn
diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c index 4f0e3ebfea4b..c88e07e2eb84 100644 --- a/arch/arm64/kernel/pci.c +++ b/arch/arm64/kernel/pci.c @@ -185,6 +185,7 @@ 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_node(sizeof(*ri), GFP_KERNEL, node); if (!ri) @@ -208,8 +209,23 @@ 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_uuid, 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); + } 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 7a4e83a8c89c..308111489b83 100644 --- a/include/linux/pci-acpi.h +++ b/include/linux/pci-acpi.h @@ -106,9 +106,10 @@ static inline void acpiphp_check_host_bridge(struct acpi_device *adev) { } #endif extern const u8 pci_acpi_dsm_uuid[]; -#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) { }
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. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- arch/arm64/kernel/pci.c | 20 ++++++++++++++++++-- include/linux/pci-acpi.h | 7 ++++--- 2 files changed, 22 insertions(+), 5 deletions(-)