Re: [dpdk-dev] [PATCH] eal: map io resources for non x86 architectures

[Thomas Monjalon <thomas.monjalon@6wind.com>]

Hi,

2015-12-17 15:37, Santosh Shukla:
> On Thu, Dec 17, 2015 at 3:32 PM, Santosh Shukla <sshukla@mvista.com> wrote:
> > On Thu, Dec 17, 2015 at 3:31 PM, Santosh Shukla <sshukla@mvista.com> wrote:
> >> On Thu, Dec 17, 2015 at 3:08 PM, Yuanhan Liu
> >> <yuanhan.liu@linux.intel.com> wrote:
> >>> On Wed, Dec 16, 2015 at 07:21:55PM +0530, Santosh Shukla wrote:
> >>>> On Wed, Dec 16, 2015 at 6:18 PM, Yuanhan Liu
> >>>> <yuanhan.liu@linux.intel.com> wrote:
> >>>> > On Wed, Dec 16, 2015 at 01:31:04PM +0100, David Marchand wrote:
> >>>> >> x86 requires a special set of instructions to access ioports, but other
> >>>> >> architectures let you remap io resources.
> >>>> >> So let eal remap io resources by accepting IORESOURCE_IO flag for
> >>>> >> architectures other than x86.
> >>>> >
> >>>> > One question: this patch could be a replacement of the igbuio_iomap patch
> >>>> > from Santosh? If so, I like it: It's more elegant.
> >>>> >
> >>>> >         --yliu
> >>>> >
> >>>>
> >>>> I did tried similar in past but not in parse_sysfs (such that
> >>>> mem.resource_addr to accept IO_RESOURCE_IO types) and observed that
> >>>> pci_map_resource not able to map address hence segfault at tespmd
> >>>> initialization.
> >>>>
> >>>> i was getting these:
> >>>> EAL: pci_map_resource(): cannot mmap(19, 0x7fa5c00000, 0x20, 0x0):
> >>>> Invalid argument (0xffffffffffffffff)
> >>>
> >>> That's because ARM (at least the kernel) doesn't allow an IO map:
> >>>
> >>> arch/arm/kernel/bios32.c
> >>> ------------------------
> >>> 618 int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
> >>> 619                         enum pci_mmap_state mmap_state, int write_combine)
> >>> 620 {
> >>> 621         if (mmap_state == pci_mmap_io)
> >>> 622                 return -EINVAL;
> >>>
> >>> And with a quick glimpse of powerpc, I see no such limitation. Hence,
> >>> this peice of code may work only on Powerpc platform (and maybe a few
> >>> others we don't care).
> >>>
> >>> So, apparently, this will not work for ARM.
> >>>
> >>
> >> Right and I did shared detailed explanation on why it wont work on
> >> this link [1], infact this patch shouldn;t work for mips too.
> >>
> >> As I mentioned earlier I did tried similar approach and so to get
> >> everything working like iomem is currently in dpdk; we need to add
> >> something like pci_remap_iospace --> ioremap_page_range() but this api
> >> not really pci_mmap_page_range types. user need to write more code on
> >> top so to use this api efficiently, also this api looks like meant to
> >> use by arch file only in kernel space.
> >>
> >>
> > missed link;
> >
> > [1] http://dpdk.org/dev/patchwork/patch/9365/
> >
> 
> IMO, it is worth keeping one special device file who could work across
> archs like arm/arm64/powerpc and others, who could map iopci bar to
> dpdk user-space. also this approach has no kernel version dependency
> too. BTW; I did mentioned in second approach in to add /dev/ioport
> interface in drivers/char/mem.c which could read more than byte in one
> single operation, but that has kernel dependency. However that
> approach too is arch agnostic.

Your first approach use an out-of-tree kernel module (igb_uio), so we cannot
really say there is no kernel dependency.
We should try to remove the need for any out-of-tree kernel module.
That's why the Linux upstream approach is a better solution.