Re: [dpdk-dev] [PATCH 6/6] virtio: arm/arm64: memory mapped IO support in pmd driver

[Santosh Shukla <sshukla@mvista.com>]

On Thu, Dec 10, 2015 at 12:34 AM, Stephen Hemminger
<stephen@networkplumber.org> wrote:
> On Thu, 10 Dec 2015 00:29:30 +0530
> Santosh Shukla <sshukla@mvista.com> wrote:
>
>> On Tue, Dec 8, 2015 at 6:23 PM, Santosh Shukla <sshukla@mvista.com> wrote:
>> >
>> >
>> > On Mon, Dec 7, 2015 at 10:38 PM, Stephen Hemminger
>> > <stephen@networkplumber.org> wrote:
>> >>
>> >> On Fri,  4 Dec 2015 23:05:19 +0530
>> >> Santosh Shukla <sshukla@mvista.com> wrote:
>> >>
>> >> >
>> >> > +#ifdef RTE_EXEC_ENV_LINUXAPP
>> >> > +/* start address of first pci_iobar slot (user-space virtual-addres) */
>> >> > +void *ioport_map;
>> >> > +#if defined(RTE_ARCH_ARM) || defined(RTE_ARCH_ARM64)
>> >> > +
>> >> > +#include <sys/mman.h>
>> >> > +#define DEV_NAME             "/dev/igb_ioport"
>> >> > +
>> >> > +/* Keeping pci_ioport_size = 4k.
>> >> > + * So maximum mmaped pci_iobar supported =
>> >> > + * (ioport_size/pci_dev->mem_resource[0].len)
>> >> > + *
>> >> > + * note: kernel could allow maximum 32 virtio-net-pci interface, that
>> >> > mean
>> >> > + * maximum 32 PCI_IOBAR(s) where each PCI_IOBAR_LEN=0x20, so
>> >> > virtio_map_ioport()
>> >> > + * func by theory gonna support 4k/0x20 ==> 128 PCI_IOBAR(s), more than
>> >> > + * max-virtio-net-pci interface.
>> >> > + */
>> >> > +#define PAGE_SIZE            4096
>> >> > +#define PCI_IOPORT_SIZE              PAGE_SIZE
>> >> > +#define PCI_IOPORT_MAX               128 /* 4k / 0x20 */
>> >> > +
>> >> > +int ioport_map_cnt;
>> >> > +#endif /* ARM, ARM64 */
>> >> > +#endif /* RTE_EXEC_ENV_LINUXAPP */
>> >>
>> >> These variables should be static.
>> >>
>> >
>> > (Sorry for delayed follow, Was travelling..)
>> > Right,
>> >
>> >>
>> >> Also, it is should be possible to extract the I/O bar stuff in a generic
>> >> way through sysfs
>> >> and not depend on a character device. The long term goal for DPDK
>> >> acceptance is to
>> >> eliminate (or at least reduce to a minumum) any requirement for special
>> >> kernel drivers.
>> >
>> >
>> > I agree. Existing implementation does read pci_iobar for start address and
>> > size, But for non-x86 arch, we need someway to map pci_iobar and thats-why
>> > thought of adding device file for a purpose, as archs like arm lack iopl()
>> > privileged io syscall support, However iopl() too quite native driver design
>> > assumption.
>> >
>> > I have few idea in my mind such that - Right now I am updating ioport_mapped
>> > addr {kernel-virtual-addr-io-memory} to /sys/bus/pci/pci_bus_xxxx/xxx/map
>> > field, instead of mapping their, I'll try to map to uio's pci interface and
>> > then use existing pci_map_resource() api to mmap kernel-virtual-io-address
>> > to user-space-virtual-ioaddr. We'll come back on this.
>> >
>>
>>
>> Spent sometime digging dpdk's uio/pci source code, Intent was to map
>> pci ioport region via uio-way. In order to achieve that I tried to
>> hack the virtio-net-pci pmd driver. Right now in virtio-net-pci case,
>> It creates two sysfs entry for pci bars: resource0 /1.
>>
>> Resource0; is ioport region
>> Resource1; is iomem region.
>>
>> By appending a RTE_PCI_DRV_NEED_MAPPING flag to drv_flag and passing
>> hw->io_base = resource1 type pci.mem_resource[slot].addr; where slot
>> =1. Resource1 is IORESOURCE_MEM type so uio/pci driver able to mmap.
>> That way I could get the valid user-space virtual address. However
>> this hack did not worked for me because at qemu side: virtio-pxe.rom
>> has virtio_headers located at ioport pci region and guest driver
>> writing at iomem region, that's why driver init failed. Note that
>> default driver doesn't use resource1 memory.
>>
>> This made me think that either I had to add dependent code in kernel
>> or something similar proposed in this patch.
>> It is because:
>> - uio driver and dependent user-space pci api's in dpdk mmaps
>> IORESOURCE_MEM types address only {refer igbuio_setup_bars() and in
>> particular function pci_parse_sysfs_resource()}.
>> - That mmap in userspace backed by arch specific api
>> pci_mmap_page_range() in kernel.
>> - pci_mmap_page_range() does not support mmaping to IO_RESOURCE_IO type memory.
>> - Having said that, we need routine or a way to to map pci_iobar
>> region from kernel virtual-address to user-space virtual address.
>
> There a couple of gotcha's with this. It turns out the iomem region
> is not mappable on some platforms. I think GCE was one of them.

afaik, In linux kernel if arch supports pci_mmap_page_range then iomem
region should map, right? I am confused by reading your reply, also I
am not aware of GCE? which platform is GCE, please suggest.