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

[Santosh Shukla <sshukla@mvista.com>]

On Thu, Dec 17, 2015 at 3:44 PM, Thomas Monjalon
<thomas.monjalon@6wind.com> wrote:
> 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.

Agree but I mentioned kernel __version__ 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.

IIUC, your suggesting archs like arm/arm64 to support io_mappe_io in
pci_mmap_page_range()?