Re: [RFC v4 1/7] PCI: Introduce domain_nr in pci_host_bridge
From: Bjorn Helgaas <helgaas@kernel.org>
Date: 2021-07-14 19:33:25
Also in:
linux-hyperv, linux-pci, lkml
On Wed, Jul 14, 2021 at 06:27:31PM +0800, Boqun Feng wrote:
Currently we retrieve the PCI domain number of the host bridge from the bus sysdata (or pci_config_window if PCI_DOMAINS_GENERIC=y). Actually we have the information at PCI host bridge probing time, and it makes sense that we store it into pci_host_bridge. One benefit of doing so is the requirement for supporting PCI on Hyper-V for ARM64, because the host bridge of Hyper-V doesn't have pci_config_window, whereas ARM64 is a PCI_DOMAINS_GENERIC=y arch, so we cannot retrieve the PCI domain number from pci_config_window on ARM64 Hyper-V guest. As the preparation for ARM64 Hyper-V PCI support, we introduce the domain_nr in pci_host_bridge and a sentinel value to allow drivers to set domain numbers properly at probing time. Currently CONFIG_PCI_DOMAINS_GENERIC=y archs are only users of this newly-introduced field.
Thanks for pushing on this. PCI_DOMAINS_GENERIC is really not very generic today and it will be good to make it more so.
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Signed-off-by: Boqun Feng <redacted> --- drivers/pci/probe.c | 6 +++++- include/linux/pci.h | 10 ++++++++++ 2 files changed, 15 insertions(+), 1 deletion(-)diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c index 79177ac37880..60c50d4f156f 100644 --- a/drivers/pci/probe.c +++ b/drivers/pci/probe.c@@ -594,6 +594,7 @@ static void pci_init_host_bridge(struct pci_host_bridge *bridge) bridge->native_pme = 1; bridge->native_ltr = 1; bridge->native_dpc = 1; + bridge->domain_nr = PCI_DOMAIN_NR_NOT_SET; device_initialize(&bridge->dev); }@@ -898,7 +899,10 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge) bus->ops = bridge->ops; bus->number = bus->busn_res.start = bridge->busnr; #ifdef CONFIG_PCI_DOMAINS_GENERIC - bus->domain_nr = pci_bus_find_domain_nr(bus, parent); + if (bridge->domain_nr == PCI_DOMAIN_NR_NOT_SET) + bus->domain_nr = pci_bus_find_domain_nr(bus, parent); + else + bus->domain_nr = bridge->domain_nr;
The domain_nr in struct pci_bus is really only used by pci_domain_nr(). It seems like it really belongs in the struct pci_host_bridge and probably doesn't need to be duplicated in the struct pci_bus. But that's probably a project for the future.
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#endif b = pci_find_bus(pci_domain_nr(bus), bridge->busnr);diff --git a/include/linux/pci.h b/include/linux/pci.h index 540b377ca8f6..952bb7d46576 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h@@ -526,6 +526,15 @@ static inline int pci_channel_offline(struct pci_dev *pdev) return (pdev->error_state != pci_channel_io_normal); } +/* + * PCI Conventional has at most 256 PCI bus segments and PCI Express has at + * most 65536 "PCI Segments Groups", therefore -1 is not a valid PCI domain
s/Segments/Segment/ Do you have a reference for these limits? I don't think either Conventional PCI or PCIe actually specifies a hardware limit on the number of domains (I think PCI uses "segment group" to mean the same thing). "Segment" in the Conventional PCI spec, r3.0, means a bus segment, which connects all the devices on a single bus. Obviously there's a limit of 256 buses under a single host bridge, but that's different concept than a domain/segment group. The PCI Firmware spec, r3.3, defines "Segment Group Number" as being in the range 0..65535, but as far as I know, that's just a firmware issue, and it applies equally to Conventional PCI and PCIe. I think you're right that -1 is a reasonable sentinel; I just don't want to claim a difference here unless there really is one.
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+ * number, and can be used as a sentinel value indicating ->domain_nr is not + * set by the driver (and CONFIG_PCI_DOMAINS_GENERIC=y can set it in generic + * code). + */ +#define PCI_DOMAIN_NR_NOT_SET (-1) + struct pci_host_bridge { struct device dev; struct pci_bus *bus; /* Root bus */@@ -533,6 +542,7 @@ struct pci_host_bridge { struct pci_ops *child_ops; void *sysdata; int busnr; + int domain_nr; struct list_head windows; /* resource_entry */ struct list_head dma_ranges; /* dma ranges resource list */ u8 (*swizzle_irq)(struct pci_dev *, u8 *); /* Platform IRQ swizzler */-- 2.30.2
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