On 2014/11/18 19:30, Arnd Bergmann wrote: > On Tuesday 18 November 2014 19:17:32 Yijing Wang wrote: >> On 2014/11/17 22:13, Arnd Bergmann wrote: >>> On Monday 17 November 2014 18:21:34 Yijing Wang wrote: >>>> This series is based Linux 3.18-rc1 and Lorenzo Pieralisi's >>>> arm PCI domain cleanup patches, link: >>>> https://patchwork.ozlabs.org/patch/407585/ >>>> >>>> Current pci scan interfaces like pci_scan_root_bus() and directly >>>> call pci_create_root_bus()/pci_scan_child_bus() lack flexiblity. >>>> Some platform infos like PCI domain and msi_chip have to be >>>> associated to PCI bus by some arch specific function. >>>> We want to make a generic pci_host_bridge, and make it hold >>>> the platform infos or hook. Then we could eliminate the lots >>>> of arch pci_domain_nr, also we could associate some platform >>>> ops something like pci_get_msi_chip(struct pci_dev *dev) >>>> with pci_host_bridge to avoid introduce arch weak functions. >>>> >>>> This RFC version not for all platforms, just applied the new >>>> scan interface in x86/arm/powerpc/ia64, I will refresh other >>>> platforms after the core pci scan interfaces are ok. >>> >>> I think overall this is a good direction to take, in particular >>> moving more things into struct pci_host_bridge so we can >>> slim down the architecture specific code. >> >> Hi Arnd, thanks very much for your review and comments! >> >>> >>> I don't particularly like the way you use the 'pci_host_info' >>> to pass callback pointers and some of the generic information. >>> This duplicates some of the issues we are currently trying >>> to untangle in the arm32 code to make drivers easier to share >>> between architectures. >> >> What arm32 code you are trying to untangle for example ? > > We have a few problems that currently prevent us from using shared > drivers across arm32 and arm64: > > - arm32 has an architecture-defined pci_sys_data structure, but > we really want to have one that is defined by the host bridge driver > and that is architecture independent. Some core functions depend > on this structure at the moment, which Lorenzo is trying to > undo > > - The pci_common_init interface on arm32 doesn't work well on > loadable drivers, it does not return an error, and it is built > around the assumption that you probe all pci host bridges at > the same time, while the standard Linux driver model assumes > that you probe one at a time. > > - The way we pass a temporary structure (hw_pci) with function pointers > into the architecture code makes it relatively hard to follow > how the initialization sequence works. > >> Introduce pci_host_info here because I want to make the PCI scan interfaces >> simple to host drviers, host drivers only need to call one scan >> interface(pci_scan_host_bridge), but from your comments, >> The combination pci_create_host_bridge() + pci_scan_xx() >> seems to be more popular. > > Yes, I think a simpler interface structure would be better than trying > to minimize the amount of code needed in drivers at the expense of > interface complexity. > >>> As a general approach, I'd rather see generic helper functions >>> being exported by the PCI core that a driver may or may not >>> call. >>> The way you split the interface between things that happen >>> before scanning the buses (pci_create_host_bridge) and >>> the actual scanning (__pci_create_root_bus, pci_scan_child_bus) >>> seems very helpful and I think we can expand that concept further: >>> >>> - The normal pci_create_host_bridge() function can contain >>> all of the DT scanning functions (finding bus/mem/io resources, >>> finding the msi-parent), while drivers that don't depend on DT >>> for this information can call the same function and fill the >>> same things after they have the pci_host_bridge pointer. >>> >>> - If a driver needs to set up mapping windows, it can do that after >>> calling pci_create_host_bridge(). E.g. all the dw_pcie glue drivers >>> can call a dw_pcie_setup_windows() function that takes the resources >>> out of the pci_host_bridge pointer before the bus is scanned. >>> >>> - The ACPI code can have a completely different way of creating >>> a struct pci_host_bridge, which is also passed into the same >>> bus scanning functions, but doesn't have to come from >>> pci_create_host_bridge. Thanks for your explanation, I will consider these problems when I refactor the core generic interfaces. >> >> I hope platforms with ACPI or DT could both use pci_create_host_bridge(). >> Why we need to use two different ways to process it ? > > These are completely different use cases: > > a) For DT, we want loadable device drivers that start by probing a host > bridge device which was added through the DT platform code. The > driver is self-contained, and eventually we want to be able to unload > it. We have lots of different per-soc drivers that require different > quirks > > b) For ACPI, the interface is defined in the ACPI spec across architectures > and SoCs, we don't have host bridge drivers and the code that initializes > the PCI is required early during boot and called from architecture > code. There is no parent device, as ACPI sees PCI as a fundamental building > block by itself, and there are no drivers because the firmware does > the initial hardware setup, so we only have to access the config space. Hmmm, I'm a little confused, so why you think ACPI host driver should not use pci_create_host_bridge(), because ACPI PCI driver has no parent device ? > > Arnd > > . > -- Thanks! Yijing -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
