On Tue, 2015-12-29 at 22:00 +0530, Santosh Shukla wrote: > On Tue, Dec 29, 2015 at 9:50 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Tuesday 29 December 2015 21:25:15 Santosh Shukla wrote: > > > mistakenly added wrong email-id of alex, looping his correct one. > > > > > > On 29 December 2015 at 21:23, Santosh Shukla <santosh.shukla@lina > > > ro.org> wrote: > > > > On 29 December 2015 at 18:58, Arnd Bergmann <arnd@xxxxxxxx> > > > > wrote: > > > > > On Wednesday 23 December 2015 17:04:40 Santosh Shukla wrote: > > > > > > On 23 December 2015 at 03:26, Arnd Bergmann <arnd@xxxxxxxx> > > > > > > wrote: > > > > > > > On Tuesday 22 December 2015, Santosh Shukla wrote: > > > > > > > > } > > > > > > > > > > > > > > > > So I care for /dev/ioport types interface who could do > > > > > > > > more than byte > > > > > > > > data copy to/from user-space. I tested this patch with > > > > > > > > little > > > > > > > > modification and could able to run pmd driver for > > > > > > > > arm/arm64 case. > > > > > > > > > > > > > > > > Like to know how to address pci_io region mapping > > > > > > > > problem for > > > > > > > > arm/arm64, in-case /dev/ioports approach is not > > > > > > > > acceptable or else I > > > > > > > > can spent time on restructuring the patch? > > > > > > > > > > > > > > > > > > > > > > For the use case you describe, can't you use the vfio > > > > > > > framework to > > > > > > > access the PCI BARs? > > > > > > > > > > > > > > > > > > > I looked at file: drivers/vfio/pci/vfio_pci.c, func > > > > > > vfio_pci_map() and > > > > > > it look to me that it only maps ioresource_mem pci region, > > > > > > pasting > > > > > > code snap: > > > > > > > > > > > > if (!(pci_resource_flags(pdev, index) & IORESOURCE_MEM)) > > > > > > return -EINVAL; > > > > > > .... > > > > > > > > > > > > and I want to map ioresource_io pci region for arm platform > > > > > > in my > > > > > > use-case. Not sure vfio maps pci_iobar region? > > > > > > > > > > Mapping I/O BARs is not portable, notably it doesn't work on > > > > > x86. > > > > > > > > > > You should be able access them using the read/write interface > > > > > on > > > > > the vfio device. > > > > > > > > > Right, x86 doesn't care as iopl() could give userspace > > > > application > > > > direct access to ioports. > > > > > > > > Also, Alex in other dpdk thread [1] suggested someone to > > > > propose io > > > > bar mapping in vfio-pci, I guess in particular to non-x86 arch > > > > so I > > > > started working on it. > > > > > > > > > > > So what's wrong with just using the existing read/write API on all > > architectures? > > > > nothing wrong, infact read/write api will still be used so to access > mmaped io pci bar at userspace. But right now vfio_pci_map() doesn't vfio_pci_mmap(), the read/write accessors fully support i/o port. > map io pci bar in particular (i.e.. ioresource_io) so I guess need to > add that bar mapping in vfio. pl. correct me if i misunderstood > anything. Maybe I misunderstood what you were asking for, it seemed like you specifically wanted to be able to mmap i/o port space, which is possible, just not something we can do on x86. Maybe I should have asked why. The vfio API already supports read/write access to i/o port space, so if you intend to mmap it only to use read/write on top of the mmap, I suppose you might see some performance improvement, but not really any new functionality. You'd also need to deal with page size issues since i/o port ranges are generally quite a bit smaller than the host page size and they'd need to be mapped such that each devices does not share a host page of i/o port space with other devices. On x86 i/o port space is mostly considered legacy and not a performance critical path for most modern devices; PCI SR-IOV specifically excludes i/o port space. So what performance gains do you expect to see in being able to mmap i/o port space and what hardware are you dealing with that relies on i/o port space rather than mmio for performance? Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
