Use the IDA infrastructure for getting a cyclic increasing ID number,
that is used for keeping track of each registered allocator per
RX-queue xdp_rxq_info.  Instead of using the IDR infrastructure, which
uses a radix tree, use a dynamic rhashtable, for creating ID to
pointer lookup table, because this is faster.

The problem that is being solved here is that, the xdp_rxq_info
pointer (stored in xdp_buff) cannot be used directly, as the
guaranteed lifetime is too short.  The info is needed on a
(potentially) remote CPU during DMA-TX completion time . In an
xdp_frame the xdp_mem_info is stored, when it got converted from an
xdp_buff, which is sufficient for the simple page refcnt based recycle
schemes.

For more advanced allocators there is a need to store a pointer to the
registered allocator.  Thus, there is a need to guard the lifetime or
validity of the allocator pointer, which is done through this
rhashtable ID map to pointer. The removal and validity of of the
allocator and helper struct xdp_mem_allocator is guarded by RCU.  The
allocator will be created by the driver, and registered with
xdp_rxq_info_reg_mem_model().

It is up-to debate who is responsible for freeing the allocator
pointer or invoking the allocator destructor function.  In any case,
this must happen via RCU freeing.

Use the IDA infrastructure for getting a cyclic increasing ID number,
that is used for keeping track of each registered allocator per
RX-queue xdp_rxq_info.

V4: Per req of Jason Wang
- Use xdp_rxq_info_reg_mem_model() in all drivers implementing
  XDP_REDIRECT, even-though it's not strictly necessary when
  allocator==NULL for type MEM_TYPE_PAGE_SHARED (given it's zero).

V6: Per req of Alex Duyck
- Introduce rhashtable_lookup() call in later patch

V8: Address sparse should be static warnings (from kbuild test robot)
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Now all the users of ndo_xdp_xmit have been converted to use xdp_return_frame.
This enable a different memory model, thus activating another code path
in the xdp_return_frame API.

V2: Fixed issues pointed out by Tariq.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Also convert driver i40e, which very recently got XDP_REDIRECT support
in commit d9314c47 ("i40e: add support for XDP_REDIRECT").

V7: This patch got added in V7 of this patchset.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

The generic xdp_frame format, was inspired by the cpumap own internal
xdp_pkt format.  It is now time to convert it over to the generic
xdp_frame format.  The cpumap needs one extra field dev_rx.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

The virtio_net driver assumes XDP frames are always released based on
page refcnt (via put_page).  Thus, is only queues the XDP data pointer
address and uses virt_to_head_page() to retrieve struct page.

Use the XDP return API to get away from such assumptions. Instead
queue an xdp_frame, which allow us to use the xdp_return_frame API,
when releasing the frame.

V8: Avoid endianness issues (found by kbuild test robot)
V9: Change __virtnet_xdp_xmit from bool to int return value (found by Dan Carpenter)
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

The tuntap driver invented it's own driver specific way of queuing
XDP packets, by storing the xdp_buff information in the top of
the XDP frame data.

Convert it over to use the more generic xdp_frame structure.  The
main problem with the in-driver method is that the xdp_rxq_info pointer
cannot be trused/used when dequeueing the frame.

V3: Remove check based on feedback from Jason
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This is needed to convert drivers tuntap and virtio_net.

This is a generalization of what is done inside cpumap, which will be
converted later.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This is done to prepare for the next patch, and it is also
nice to move this XDP related struct out of filter.h.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Extend struct ixgbe_tx_buffer to store the xdp_mem_info.

Notice that this could be optimized further by putting this into
a union in the struct ixgbe_tx_buffer, but this patchset
works towards removing this again.  Thus, this is not done.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Introduce an xdp_return_frame API, and convert over cpumap as
the first user, given it have queued XDP frame structure to leverage.

V3: Cleanup and remove C99 style comments, pointed out by Alex Duyck.
V6: Remove comment that id will be added later (Req by Alex Duyck)
V8: Rename enum mem_type to xdp_mem_type (found by kbuild test robot)
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This implements basic XDP redirect support in mlx5 driver.

Notice that the ndo_xdp_xmit() is NOT implemented, because that API
need some changes that this patchset is working towards.

The main purpose of this patch is have different drivers doing
XDP_REDIRECT to show how different memory models behave in a cross
driver world.

Update(pre-RFCv2 Tariq): Need to DMA unmap page before xdp_do_redirect,
as the return API does not exist yet to to keep this mapped.

Update(pre-RFCv3 Saeed): Don't mix XDP_TX and XDP_REDIRECT flushing,
introduce xdpsq.db.redirect_flush boolian.

V9: Adjust for commit 121e8927 ("net/mlx5e: Refactor RQ XDP_TX indication")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1. Added red_drops stats. Inbound packets dropped by RED, buffer exhaustion
2. Included fcs_err, jabber_err, l2_err and frame_err errors under
   rx_errors
3. Included fifo_err, dmac_drop, red_drops, fw_err_pko, fw_err_link and
   fw_err_drop under rx_dropped
4. Included max_collision_fail, max_deferral_fail, total_collisions,
   fw_err_pko, fw_err_link, fw_err_drop and fw_err_pki under tx_dropped
5. Counting dma mapping errors
6. Added some firmware stats description and removed for some
Signed-off-by: Intiyaz Basha <intiyaz.basha@cavium.com>
Acked-by: Derek Chickles <derek.chickles@cavium.com>
Acked-by: Satanand Burla <satananda.burla@cavium.com>
Signed-off-by: Felix Manlunas <felix.manlunas@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This tracepoint was replaced by inet_sock_set_state in 563e0bb0 and not
used anywhere in the kernel anymore. Remove it.
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Heiner Kallweit says:

====================
PCI: add two more values for PCIe Max_Read_Request_Size and initially use them in r8169 network driver

In r8169 network driver I stumbled across a magic number translating
to PCI MRRS size 4K. The PCI core is still missing constants for
values 2K and 4K (as defined in PCI standard).

So let's add these two constants and use the 4K constant in r8169.

Second patch depends on the first one, therefore both patches
preferrably should go through either PCI or netdev tree.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Replace magic number "0x5 << MAX_READ_REQUEST_SHIFT" with the
appropriate constant as defined in PCI core.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This patch adds missing values for the max read request size.
E.g. network driver r8169 uses a value of 4K.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Jose Abreu says:

====================
net: stmmac: Stop using hard-coded callbacks

This a starting point for a cleanup and re-organization of stmmac.

In this series we stop using hard-coded callbacks along the code and use
instead helpers which are defined in a single place ("hwif.h").

This brings several advantages:
	1) Less typing :)
	2) Guaranteed function pointer check
	3) More flexibility

By 2) we stop using the repeated pattern of:
	if (priv->hw->mac->some_func)
		priv->hw->mac->some_func(...)

I didn't check but I expect the final .ko will be bigger with this series
because *all* of function pointers are checked.

Anyway, I hope this can make the code more readable and more flexible now.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Switch stmmac_mode_ops to generic Hardware Interface Helpers instead of
using hard-coded callbacks. This makes the code more readable and more
flexible.

No functional change.
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Joao Pinto <jpinto@synopsys.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Switch stmmac_hwtimestamp to generic Hardware Interface Helpers instead
of using hard-coded callbacks. This makes the code more readable and
more flexible.

No functional change.
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Joao Pinto <jpinto@synopsys.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Switch stmmac_ops to generic Hardware Interface Helpers instead of using
hard-coded callbacks. This makes the code more readable and more
flexible.

No functional change.
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Joao Pinto <jpinto@synopsys.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Switch stmmac_dma_ops to generic Hardware Interface Helpers instead of
using hard-coded callbacks. This makes the code more readable and more
flexible.

No functional change.
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Joao Pinto <jpinto@synopsys.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Switch stmmac_desc_ops to generic Hardware Interface Helpers instead of
using hard-coded callbacks. This makes the code more readable and more
flexible.

No functional change.
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Joao Pinto <jpinto@synopsys.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Eric Dumazet says:

====================
tcp: add zero copy receive

This patch series add mmap() support to TCP sockets for RX zero copy.

While tcp_mmap() patch itself is quite small (~100 LOC), optimal support
for asynchronous mmap() required better SO_RCVLOWAT behavior, and a
test program to demonstrate how mmap() on TCP sockets can be used.

Note that mmap() (and associated munmap()) calls are adding more
pressure on per-process VM semaphore, so might not show benefit
for processus with high number of threads.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

This is a reference program showing how mmap() can be used
on TCP flows to implement receive zero copy.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Some networks can make sure TCP payload can exactly fit 4KB pages,
with well chosen MSS/MTU and architectures.

Implement mmap() system call so that applications can avoid
copying data without complex splice() games.

Note that a successful mmap( X bytes) on TCP socket is consuming
bytes, as if recvmsg() has been done. (tp->copied += X)

Only PROT_READ mappings are accepted, as skb page frags
are fundamentally shared and read only.

If tcp_mmap() finds data that is not a full page, or a patch of
urgent data, -EINVAL is returned, no bytes are consumed.

Application must fallback to recvmsg() to read the problematic sequence.

mmap() wont block,  regardless of socket being in blocking or
non-blocking mode. If not enough bytes are in receive queue,
mmap() would return -EAGAIN, or -EIO if socket is in a state
where no other bytes can be added into receive queue.

An application might use SO_RCVLOWAT, poll() and/or ioctl( FIONREAD)
to efficiently use mmap()

On the sender side, MSG_EOR might help to clearly separate unaligned
headers and 4K-aligned chunks if necessary.

Tested:

mlx4 (cx-3) 40Gbit NIC, with tcp_mmap program provided in following patch.
MTU set to 4168  (4096 TCP payload, 40 bytes IPv6 header, 32 bytes TCP header)

Without mmap() (tcp_mmap -s)

received 32768 MB (0 % mmap'ed) in 8.13342 s, 33.7961 Gbit,
  cpu usage user:0.034 sys:3.778, 116.333 usec per MB, 63062 c-switches
received 32768 MB (0 % mmap'ed) in 8.14501 s, 33.748 Gbit,
  cpu usage user:0.029 sys:3.997, 122.864 usec per MB, 61903 c-switches
received 32768 MB (0 % mmap'ed) in 8.11723 s, 33.8635 Gbit,
  cpu usage user:0.048 sys:3.964, 122.437 usec per MB, 62983 c-switches
received 32768 MB (0 % mmap'ed) in 8.39189 s, 32.7552 Gbit,
  cpu usage user:0.038 sys:4.181, 128.754 usec per MB, 55834 c-switches

With mmap() on receiver (tcp_mmap -s -z)

received 32768 MB (100 % mmap'ed) in 8.03083 s, 34.2278 Gbit,
  cpu usage user:0.024 sys:1.466, 45.4712 usec per MB, 65479 c-switches
received 32768 MB (100 % mmap'ed) in 7.98805 s, 34.4111 Gbit,
  cpu usage user:0.026 sys:1.401, 43.5486 usec per MB, 65447 c-switches
received 32768 MB (100 % mmap'ed) in 7.98377 s, 34.4296 Gbit,
  cpu usage user:0.028 sys:1.452, 45.166 usec per MB, 65496 c-switches
received 32768 MB (99.9969 % mmap'ed) in 8.01838 s, 34.281 Gbit,
  cpu usage user:0.02 sys:1.446, 44.7388 usec per MB, 65505 c-switches
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

SO_RCVLOWAT is properly handled in tcp_poll(), so that POLLIN is only
generated when enough bytes are available in receive queue, after
David change (commit c7004482 "tcp: Respect SO_RCVLOWAT in tcp_poll().")

But TCP still calls sk->sk_data_ready() for each chunk added in receive
queue, meaning thread is awaken, and goes back to sleep shortly after.

Tested:

tcp_mmap test program, receiving 32768 MB of data with SO_RCVLOWAT set to 512KB

-> Should get ~2 wakeups (c-switches) per MB, regardless of how many
(tiny or big) packets were received.

High speed (mostly full size GRO packets)

received 32768 MB (100 % mmap'ed) in 8.03112 s, 34.2266 Gbit,
  cpu usage user:0.037 sys:1.404, 43.9758 usec per MB, 65497 c-switches

received 32768 MB (99.9954 % mmap'ed) in 7.98453 s, 34.4263 Gbit,
  cpu usage user:0.03 sys:1.422, 44.3115 usec per MB, 65485 c-switches

Low speed (sender is ratelimited and sends 1-MSS at a time, so GRO is not helping)

received 22474.5 MB (100 % mmap'ed) in 6015.35 s, 0.0313414 Gbit,
  cpu usage user:0.05 sys:1.586, 72.7952 usec per MB, 44950 c-switches
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

We should not delay acks if there are not enough bytes
in receive queue to satisfy SO_RCVLOWAT.

Since [E]POLLIN event is not going to be generated, there is little
hope for a delayed ack to be useful.

In fact, delaying ACK prevents sender from completing
the transfer.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Applications might use SO_RCVLOWAT on TCP socket hoping to receive
one [E]POLLIN event only when a given amount of bytes are ready in socket
receive queue.

Problem is that receive autotuning is not aware of this constraint,
meaning sk_rcvbuf might be too small to allow all bytes to be stored.

Add a new (struct proto_ops)->set_rcvlowat method so that a protocol
can override the default setsockopt(SO_RCVLOWAT) behavior.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Roman Mashak <mrv@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Remove unnecessary check on update_lft variable in
addrconf_prefix_rcv_add_addr routine since it is always set to 0.
Moreover remove update_lft re-initialization to 0
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

When the interface is down, head/tail of the descriptor
ring address is set to 0 in netsec_netdev_stop().
But netsec hardware still keeps the previous descriptor
ring address, so there is inconsistency between driver
and hardware after interface is up at a later time.
To address this inconsistency, add netsec_reset_hardware()
when the interface is down.

In addition, to minimize the reset process,
add flag to decide whether driver loads the netsec microcode.
Even if driver resets the netsec hardware, netsec microcode
keeps resident on RAM, so it is ok we only load the microcode
at initialization.

This patch is critical for installation over network.
Signed-off-by: Masahisa KOJIMA <masahisa.kojima@linaro.org>
Fixes: 533dd11a ("net: socionext: Add Synquacer NetSec driver")
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Enable TX-irq as well during ndo_open() as we can not count upon
RX to arrive early enough to trigger the napi. This patch is critical
for installation over network.

Fixes: 533dd11a ("net: socionext: Add Synquacer NetSec driver")
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

The usage of of_device_get_match_data() reduce the code size a bit.

Also, the only way to call mtk_probe() is to match an entry in
of_mtk_match[], so match cannot be NULL.
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Pull networking fixes from David Miller:

 1) In ip_gre tunnel, handle the conflict between TUNNEL_{SEQ,CSUM} and
    GSO/LLTX properly. From Sabrina Dubroca.

 2) Stop properly on error in lan78xx_read_otp(), from Phil Elwell.

 3) Don't uncompress in slip before rstate is initialized, from Tejaswi
    Tanikella.

 4) When using 1.x firmware on aquantia, issue a deinit before we
    hardware reset the chip, otherwise we break dirty wake WOL. From
    Igor Russkikh.

 5) Correct log check in vhost_vq_access_ok(), from Stefan Hajnoczi.

 6) Fix ethtool -x crashes in bnxt_en, from Michael Chan.

 7) Fix races in l2tp tunnel creation and duplicate tunnel detection,
    from Guillaume Nault.

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net: (22 commits)
  l2tp: fix race in duplicate tunnel detection
  l2tp: fix races in tunnel creation
  tun: send netlink notification when the device is modified
  tun: set the flags before registering the netdevice
  lan78xx: Don't reset the interface on open
  bnxt_en: Fix NULL pointer dereference at bnxt_free_irq().
  bnxt_en: Need to include RDMA rings in bnxt_check_rings().
  bnxt_en: Support max-mtu with VF-reps
  bnxt_en: Ignore src port field in decap filter nodes
  bnxt_en: do not allow wildcard matches for L2 flows
  bnxt_en: Fix ethtool -x crash when device is down.
  vhost: return bool from *_access_ok() functions
  vhost: fix vhost_vq_access_ok() log check
  vhost: Fix vhost_copy_to_user()
  net: aquantia: oops when shutdown on already stopped device
  net: aquantia: Regression on reset with 1.x firmware
  cdc_ether: flag the Cinterion AHS8 modem by gemalto as WWAN
  slip: Check if rstate is initialized before uncompressing
  lan78xx: Avoid spurious kevent 4 "error"
  lan78xx: Correctly indicate invalid OTP
  ...

Pull xen fixes from Juergen Gross:
 "A few fixes of Xen related core code and drivers"

* tag 'for-linus-4.17-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
  xen/pvh: Indicate XENFEAT_linux_rsdp_unrestricted to Xen
  xen/acpi: off by one in read_acpi_id()
  xen/acpi: upload _PSD info for non Dom0 CPUs too
  x86/xen: Delay get_cpu_cap until stack canary is established
  xen: xenbus_dev_frontend: Verify body of XS_TRANSACTION_END
  xen: xenbus: Catch closing of non existent transactions
  xen: xenbus_dev_frontend: Fix XS_TRANSACTION_END handling

Pull dma-mapping fix from Christoph Hellwig:
 "Fix for one swiotlb regression in 2.16 from Takashi"

* tag 'dma-mapping-4.17-2' of git://git.infradead.org/users/hch/dma-mapping:
  swiotlb: fix unexpected swiotlb_alloc_coherent failures

Pull MMC fixes from Ulf Hansson:
 "MMC core:
   - Prevent bus reference leak in mmc_blk_init()

  MMC host:
   - tmio: Fix error handling when issuing CMD23
   - jz4740: Fix race condition in IRQ mask update"

* tag 'mmc-v4.17-2' of git://git.kernel.org/pub/scm/linux/kernel/git/ulfh/mmc:
  mmc: tmio: Fix error handling when issuing CMD23
  mmc: core: Prevent bus reference leak in mmc_blk_init()
  mmc: jz4740: Fix race condition in IRQ mask update

Pull kdb updates from Jason Wessel:

 - fix 2032 time access issues and new compiler warnings

 - minor regression test cleanup

 - formatting fixes for end user use of kdb

* tag 'for_linus-4.16' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/kgdb:
  kdb: use memmove instead of overlapping memcpy
  kdb: use ktime_get_mono_fast_ns() instead of ktime_get_ts()
  kdb: bl: don't use tab character in output
  kdb: drop newline in unknown command output
  kdb: make "mdr" command repeat
  kdb: use __ktime_get_real_seconds instead of __current_kernel_time
  misc: kgdbts: Display progress of asynchronous tests

Pull microblaze updates from Michal Simek:
 "Use generic pci_mmap_resource_range()"

* tag 'microblaze-4.17-rc1' of git://git.monstr.eu/linux-2.6-microblaze:
  microblaze: Use generic pci_mmap_resource_range()
  microblaze: Provide pgprot_device/writecombine macros for nommu

Pull asm-generic fixes from Arnd Bergmann:
 "I have one regression fix for a minor build problem after the
  architecture removal series, plus a rework of the barriers in the
  readl/writel functions, thanks to work by Sinan Kaya:

  This started from a discussion on the linuxpcc and rdma mailing
  lists[1]. To summarize, we decided that architectures are responsible
  to serialize readl() and writel() accesses on a device MMIO space
  relative to DMA performed by that device.

  This series provides a pessimistic implementation of that behavior for
  asm-generic/io.h, which is in turn used by a number of architectures
  (h8300, microblaze, nios2, openrisc, s390, sparc, um, unicore32, and
  xtensa). Some of those presumably need no extra barriers, or something
  weaker than rmb()/wmb(), and they are advised to override the new
  default for better performance.

  For inb()/outb(), the same barriers are used, but architectures might
  want to add another barrier to outb() here if that can guarantee
  non-posted behavior (some architectures can, others cannot do that).

  The readl_relaxed()/writel_relaxed() family of functions retains the
  existing behavior with no extra barriers"

[1] https://lists.ozlabs.org/pipermail/linuxppc-dev/2018-March/170481.html

* tag 'asm-generic' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic:
  io: change writeX_relaxed() to remove barriers
  io: change readX_relaxed() to remove barriers
  dts: remove cris & metag dts hard link file
  io: change inX() to have their own IO barrier overrides
  io: change outX() to have their own IO barrier overrides
  io: define stronger ordering for the default writeX() implementation
  io: define stronger ordering for the default readX() implementation
  io: define several IO & PIO barrier types for the asm-generic version