On Tuesday 04 February 2014 11:09:22 Liviu Dudau wrote: > On Tue, Feb 04, 2014 at 08:44:36AM +0000, Arnd Bergmann wrote: > > Well, I/O space never starts at physical zero in reality, so it is > > broken in practice. The CONFIG_GENERIC_IOMAP option tries to solve > > the problem of I/O spaces that are not memory mapped, which is > > actually quite rare (x86, ia64, some rare powerpc bridges, and possibly > > Alpha). The norm is that if you have I/O space, it is memory mapped > > and you don't need GENERIC_IOMAP. I think most of the architectures > > selecting GENERIC_IOMAP have incorrectly copied that from x86. > > If you are talking about CPU addresses for I/O space, then you are (mostly?) right. > I've seen some code in powerpc that tries to handle the case where I/O starts at zero. > > For MMIO, yes, it would be crazy to start at CPU address zero. But, > the ioport_map takes a port number, and those do start at zero, right? What I meant is that asm-generic/io.h assumes that the I/O ports are mapped at /virtual/ address zero, which is even more crazy, since that is normally in user space. Sorry for confusing it with physical address zero. Now the GENERIC_IOMAP uses a similar fiction by defining that virtual address token 0x10000-0x1ffff are used to access I/O space when calling inb/outb, but that is something you only need to do when you have no memory mapped I/O port. Some older ARM platforms (PXA for instance) also defined the I/O space to start at virtual address zero, and use a per-bus io_offset that was equal to the ioremapped I/O window. This actually works, but it means that the logical port numbers are all high, and you have to set IO_SPACE_LIMIT to ULONG_MAX, and it breaks horribly for any driver that tries to store a port number in a type that is shorter than 'unsigned long'. We definitely don't want to do this for new code. > > > My main concern with the existing API is the requirement to have a subsys_initcall > > > in your host bridge or mach code, due to the way the initialisation is done (you > > > need the DT code to probe your driver, but you cannot start the scanning of the > > > PCI bus until the arch code is initialised, so it gets deferred via > > > subsys_initcall when it calls pci_common_init). I bet that if one tries to > > > instantiate a Tegra PCI host bridge controller on a Marvell platform things will > > > break pretty quickly (random example here). > > > > I'm not following here. All the new host controller drivers should > > be platform drivers that only bind to the host devices in DT > > that are present. Both mvebu and tegra use a normal "module_platform_driver" > > for initialization, not a "subsys_initcall". > > I was actually looking at mach-dove, I thought that was Marvell as well. mach-dove is going away soon, it will get merged into mach-mvebu and then use drivers/pci/host/pci-mvebu.c > But both mvebu and tegra call pci_common_init_dev. The busnr gets assigned based on > the registration order. I wonder if any of the host bridge code copes with having > assigned a bus number other than zero for its "root bus". I think all "new" host bridges now use nr_controllers=1, which means that you always start at but number zero and use PCI domain if you have multiple independent root bridges. > > > > Right. I guess we can support both interfaces on ARM32 for the forseeable > > future (renaming the new one) and just change the existing implementation > > to update the bitmap. Any cross-platform host controller driver would > > have to use the new interface however. > > OK, I can try to add the function to my patch. Call it pci_ioremap_iores? Sounds ok, I can't think of anything better at least. Arnd -- 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
