On Mon, Mar 10, 2014 at 07:59:59PM +0100, Arnd Bergmann wrote: > On Monday 10 March 2014 16:33:44 Liviu Dudau wrote: > > On Mon, Mar 10, 2014 at 03:21:01PM +0000, Arnd Bergmann wrote: > > > On Monday 10 March 2014 14:44:14 Liviu Dudau wrote: > > > > I will try to improve the error handling in the next patchset version. > > > > However I am still confused about the earlier discussion on > > > > pci_register_io_range(). Your suggestion initially was to return an > > > > error in the default weak implementation, but in your last email you > > > > are talking about returning 'port'. > > > > > > You can do either one: 'port' should be positive or zero, while the > > > error would always be negative. We do the same thing in many interfaces > > > in the kernel. > > > > > > > My idea when I've introduced the > > > > helper function was that it would return an error if it fails to > > > > register the IO range and zero otherwise. I agree that we can treat > > > > the default 'do nothing with the IO range' case as an error, with > > > > the caveat that will force architectures that use this code to > > > > provide their own implementation of pci_register_io_range() in order > > > > to avoid failure, even for the cases where the architecture has a 1:1 > > > > mapping between IO and CPU addresses. > > > > > > Which architectures are you thinking of? The only one I know that > > > does this is ia64, and we won't ever have to support this helper > > > on that architecture. > > > > I was thinking about architectures that have IO_SPACE_LIMIT >= 0xffffffff. > > While not an absolute indicator, with the default pci_address_to_pio() > > that means that they can use the CPU MMIO address as IO address directly. > > Not really, that would only work if they also have instructions to do > raw accesses to physical memory addresses rather than virtual memory > pointers that most architectures do. > > > $ git grep IO_SPACE_LIMIT | grep -i ffffffff > > arch/arm/include/asm/io.h:#define IO_SPACE_LIMIT ((resource_size_t)0xffffffff) > > arch/arm/mach-at91/include/mach/io.h:#define IO_SPACE_LIMIT 0xFFFFFFFF > > arch/arm/mach-omap1/include/mach/io.h:#define IO_SPACE_LIMIT 0xffffffff > > arch/arm/mach-pxa/include/mach/io.h:#define IO_SPACE_LIMIT 0xffffffff > > arch/arm/mach-s3c24xx/include/mach/io.h:#define IO_SPACE_LIMIT 0xffffffff > > These use a special trick where an __iomem pointer is the same as > the port number. This works most of the time, but breaks anything > that assumes that port numbers are low, such as /dev/port or > broken devices. Moreover, it means your code won't work because > it depends on passing the virtual start address of the PIO mapping > window as io_offset. > > > arch/avr32/include/asm/io.h:#define IO_SPACE_LIMIT 0xffffffff > > arch/frv/include/asm/io.h:#define IO_SPACE_LIMIT 0xffffffff > > They have no MMU, and the code relies on the port number to match > both the virtual and the physical address. You could be right about > these, but I would guess that the code also needs some other > changes if we want to make it work on nommu kernels. It also depends > on whether the I/O bus address is the same as the CPU address, or > if it starts at bus address 0. > > > arch/ia64/include/asm/io.h:#define IO_SPACE_LIMIT 0xffffffffffffffffUL > > Here, the definition is special, the token is just used to encode > a space number and an offset within the I/O space. > > > arch/m32r/include/asm/io.h:#define IO_SPACE_LIMIT 0xFFFFFFFF > > no PCI here. > > > arch/m68k/include/asm/io_no.h:#define IO_SPACE_LIMIT 0xffffffff > > This looks like a mistake, it should be smaller > > > arch/microblaze/include/asm/io.h:#define IO_SPACE_LIMIT (0xFFFFFFFF) > > I suspect it doesn't actually work. microblaze copied large parts > of this from PowerPC, but the parts that differ apparently get > it wrong for the I/O space. > > > arch/mn10300/include/asm/io.h:#define IO_SPACE_LIMIT 0xffffffff > > Same category as frv. We should ask David Howells whether he > thinks I/O space actually works on these. > > > arch/sh/include/asm/io.h:#define IO_SPACE_LIMIT 0xffffffff > > I think this should just be 0xffff. > > > arch/sparc/include/asm/io_32.h:#define IO_SPACE_LIMIT 0xffffffff > > arch/sparc/include/asm/io_64.h:#define IO_SPACE_LIMIT 0xffffffffffffffffUL > > Sparc actually accesses the physical addresses, so in theory > it could always work. In the 64-bit case it would however have > to check that the port number is smaller than 0xffffffff, otherwise > you couldn't set the BAR. This means you still need a custom > function. > > > arch/tile/include/asm/io.h:#define IO_SPACE_LIMIT 0xffffffff > > tile seems to support only ioport_map() but not inb/outb, if I'm > reading this right. > > > > I did not ask to treat 'do nothing with the IO range' as an error, > > > what I meant is that we should treat 'architecture cannot translate > > > from I/O space to memory space but DT lists a translation anyway' > > > as an error. On x86, you should never see an entry for the I/O space > > > in "ranges", so we will not call this function unless there is a > > > bug in DT. > > > > Ok, it's just that there is no "architecture cannot translate from I/O > > space to memory space" indicator anywhere and I don't want to make x86 > > a special case. > > Right. > > > So, my proposal is this: default weak implementation of pci_register_io_range() > > returns an error (meaning I have no idea how to translate IO addresses > > to memory space) and anyone that wants this function to return success will > > have to provide their implementation. > > Another idea: make this conditional on the definition of PCI_IOBASE: If this > is defined, we can use the arm64 version that uses this number. Otherwise > we fall back to returning an error, which means that either on the > architecture we shouldn't be calling that function, or we need a custom > implementation. PCI_IOBASE is always defined. See the discussion with Russell on this subject. include/asm-generic/io.h has at line 118: #ifndef PCI_IOBASE #define PCI_IOBASE ((void __iomem *) 0) #endif I will go with my idea tomorrow. arm64 overwrite the implementation anyway, I find it cleaner rather than having to do #ifdefs and/or ifs. Best regards, Liviu > > 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 > -- 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
