Eric Dumazet says:

====================
gro: get out of core files

Move GRO related content into net/core/gro.c
and include/net/gro.h.

This reduces GRO scope to where it is really needed,
and shrinks too big files (include/linux/netdevice.h
and net/core/dev.c)
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

Move gro code and data from net/core/dev.c to net/core/gro.c
to ease maintenance.

gro_normal_list() and gro_normal_one() are inlined
because they are called from both files.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/gro.c will contain all core gro functions,
to shrink net/core/skbuff.c and net/core/dev.c

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This helper is used once, no need to keep it in fat net/core/skbuff.c

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h became too big, move gro stuff
into include/net/gro.h

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Eric Dumazet says:

====================
tcp: optimizations for linux-5.17

Mostly small improvements in this series.

The notable change is in "defer skb freeing after
socket lock is released" in recvmsg() (and RX zerocopy)

The idea is to try to let skb freeing to BH handler,
whenever possible, or at least perform the freeing
outside of the socket lock section, for much improved
performance. This idea can probably be extended
to other protocols.

 Tests on a 100Gbit NIC
 Max throughput for one TCP_STREAM flow, over 10 runs.

 MTU : 1500  (1428 bytes of TCP payload per MSS)
 Before: 55 Gbit
 After:  66 Gbit

 MTU : 4096+ (4096 bytes of TCP payload, plus TCP/IPv6 headers)
 Before: 82 Gbit
 After:  95 Gbit
====================

Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

sk_rx_dst/sk_rx_dst_ifindex/sk_rx_dst_cookie are read in early demux,
and currently spans two cache lines.

Moving them close to sk_refcnt makes more sense, as only one cache
line is needed.

New layout for this hot cache line is :

struct sock {
	struct sock_common         __sk_common;          /*     0  0x88 */
	/* --- cacheline 2 boundary (128 bytes) was 8 bytes ago --- */
	struct dst_entry *         sk_rx_dst;            /*  0x88   0x8 */
	int                        sk_rx_dst_ifindex;    /*  0x90   0x4 */
	u32                        sk_rx_dst_cookie;     /*  0x94   0x4 */
	socket_lock_t              sk_lock;              /*  0x98  0x20 */
	atomic_t                   sk_drops;             /*  0xb8   0x4 */
	int                        sk_rcvlowat;          /*  0xbc   0x4 */
	/* --- cacheline 3 boundary (192 bytes) --- */

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Under pressure, tcp recvmsg() has logic to process the socket backlog,
but calls tcp_cleanup_rbuf() right before.

Avoiding sending ACK right before processing new segments makes
a lot of sense, as this decrease the number of ACK packets,
with no impact on effective ACK clocking.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Testing timeo before sk_err/sk_state/sk_shutdown makes more sense.

Modern applications use non-blocking IO, while a socket is terminated
only once during its life time.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tcp recvmsg() (or rx zerocopy) spends a fair amount of time
freeing skbs after their payload has been consumed.

A typical ~64KB GRO packet has to release ~45 page
references, eventually going to page allocator
for each of them.

Currently, this freeing is performed while socket lock
is held, meaning that there is a high chance that
BH handler has to queue incoming packets to tcp socket backlog.

This can cause additional latencies, because the user
thread has to process the backlog at release_sock() time,
and while doing so, additional frames can be added
by BH handler.

This patch adds logic to defer these frees after socket
lock is released, or directly from BH handler if possible.

Being able to free these skbs from BH handler helps a lot,
because this avoids the usual alloc/free assymetry,
when BH handler and user thread do not run on same cpu or
NUMA node.

One cpu can now be fully utilized for the kernel->user copy,
and another cpu is handling BH processing and skb/page
allocs/frees (assuming RFS is not forcing use of a single CPU)

Tested:
 100Gbit NIC
 Max throughput for one TCP_STREAM flow, over 10 runs

MTU : 1500
Before: 55 Gbit
After:  66 Gbit

MTU : 4096+(headers)
Before: 82 Gbit
After:  95 Gbit

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

TCP uses sk_eat_skb() when skbs can be removed from receive queue.
However, the call to skb_orphan() from __kfree_skb() incurs
an indirect call so sock_rfee(), which is more expensive than
a direct call, especially for CONFIG_RETPOLINE=y.

Add tcp_eat_recv_skb() function to make the call before
__kfree_skb().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Use some unlikely() hints in the fast path.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tcp_poll() and tcp_ioctl() are reading tp->urg_data without socket lock
owned.

Also, it is faster to first check tp->urg_data in tcp_poll(),
then tp->urg_seq == tp->copied_seq, because tp->urg_seq is
located in a different/cold cache line.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tcp_segs_in() can be called from BH, while socket spinlock
is held but socket owned by user, eventually reading these
fields from tcp_get_info()

Found by code inspection, no need to backport this patch
to older kernels.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Use INDIRECT_CALL_INET() to avoid an indirect call
when/if CONFIG_RETPOLINE=y

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

When reading large chunks of data, incoming packets might
be added to the backlog from BH.

tcp recvmsg() detects the backlog queue is not empty, and uses
a release_sock()/lock_sock() pair to process this backlog.

We now have __sk_flush_backlog() to perform this
a bit faster.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tcp_memory_allocated and tcp_sockets_allocated often share
a common cache line, source of false sharing.

Also take care of udp_memory_allocated and mptcp_sockets_allocated.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

(struct proto)->sk_forward_alloc is currently only used by MPTCP.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Move sk_bind_phc next to sk_peer_lock to fill a hole.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

gso_size can be moved after tclass, to use an existing hole.
(8 bytes saved on 64bit arches)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Instead of using a full netdev_features_t, we can use a single bit,
as sk_route_nocaps is only used to remove NETIF_F_GSO_MASK from
sk->sk_route_cap.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

We were only using one bit, and we can replace it by sk_is_tcp()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Move sk_is_tcp() to include/net/sock.h and use it where we can.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

For TCP flows, inet6_sk(sk)->saddr has the same value
than sk->sk_v6_rcv_saddr.

Using sk->sk_v6_rcv_saddr increases data locality.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

For some reason, I forgot to change __tcp_v6_send_check() at
the same time I removed (ip_summed == CHECKSUM_PARTIAL) check
in __tcp_v4_send_check()

Fixes: 98be9b12

 ("tcp: remove dead code after CHECKSUM_PARTIAL adoption")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

If packet is going to be coalesced, sk_sndbuf/sk_rcvbuf values
are not used. Defer their access to the point we need them.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

There were several cases where validate() would return bogus supported
modes with unusual combinations of interfaces and capabilities. For
example, if state->interface was 10GBASER and the macb had HIGH_SPEED
and PCS but not GIGABIT MODE, then 10/100 modes would be set anyway. In
another case, SGMII could be enabled even if the mac was not a GEM
(despite this being checked for later on in mac_config()). These
inconsistencies make it difficult to refactor this function cleanly.

There is still the open question of what exactly the requirements for
SGMII and 10GBASER are, and what SGMII actually supports. If someone
from Cadence (or anyone else with access to the GEM/MACB datasheet)
could comment on this, it would be greatly appreciated. In particular,
what is supported by Cadence vs. vendor extension/limitation?

To address this, the current logic is split into three parts. First, we
determine what we support, then we eliminate unsupported interfaces, and
finally we set the appropriate link modes. There is still some cruft
related to NA, but this can be removed in a future patch.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Parshuram Thombare <pthombar@cadence.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20211112190400.1937855-1-sean.anderson@seco.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Daniel Borkmann says:

====================
pull-request: bpf-next 2021-11-15

We've added 72 non-merge commits during the last 13 day(s) which contain
a total of 171 files changed, 2728 insertions(+), 1143 deletions(-).

The main changes are:

1) Add btf_type_tag attributes to bring kernel annotations like __user/__rcu to
   BTF such that BPF verifier will be able to detect misuse, from Yonghong Song.

2) Big batch of libbpf improvements including various fixes, future proofing APIs,
   and adding a unified, OPTS-based bpf_prog_load() low-level API, from Andrii Nakryiko.

3) Add ingress_ifindex to BPF_SK_LOOKUP program type for selectively applying the
   programmable socket lookup logic to packets from a given netdev, from Mark Pashmfouroush.

4) Remove the 128M upper JIT limit for BPF programs on arm64 and add selftest to
   ensure exception handling still works, from Russell King and Alan Maguire.

5) Add a new bpf_find_vma() helper for tracing to map an address to the backing
   file such as shared library, from Song Liu.

6) Batch of various misc fixes to bpftool, fixing a memory leak in BPF program dump,
   updating documentation and bash-completion among others, from Quentin Monnet.

7) Deprecate libbpf bpf_program__get_prog_info_linear() API and migrate its users as
   the API is heavily tailored around perf and is non-generic, from Dave Marchevsky.

8) Enable libbpf's strict mode by default in bpftool and add a --legacy option as an
   opt-out for more relaxed BPF program requirements, from Stanislav Fomichev.

9) Fix bpftool to use libbpf_get_error() to check for errors, from Hengqi Chen.

* https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next: (72 commits)
  bpftool: Use libbpf_get_error() to check error
  bpftool: Fix mixed indentation in documentation
  bpftool: Update the lists of names for maps and prog-attach types
  bpftool: Fix indent in option lists in the documentation
  bpftool: Remove inclusion of utilities.mak from Makefiles
  bpftool: Fix memory leak in prog_dump()
  selftests/bpf: Fix a tautological-constant-out-of-range-compare compiler warning
  selftests/bpf: Fix an unused-but-set-variable compiler warning
  bpf: Introduce btf_tracing_ids
  bpf: Extend BTF_ID_LIST_GLOBAL with parameter for number of IDs
  bpftool: Enable libbpf's strict mode by default
  docs/bpf: Update documentation for BTF_KIND_TYPE_TAG support
  selftests/bpf: Clarify llvm dependency with btf_tag selftest
  selftests/bpf: Add a C test for btf_type_tag
  selftests/bpf: Rename progs/tag.c to progs/btf_decl_tag.c
  selftests/bpf: Test BTF_KIND_DECL_TAG for deduplication
  selftests/bpf: Add BTF_KIND_TYPE_TAG unit tests
  selftests/bpf: Test libbpf API function btf__add_type_tag()
  bpftool: Support BTF_KIND_TYPE_TAG
  libbpf: Support BTF_KIND_TYPE_TAG
  ...
====================

Link: https://lore.kernel.org/r/20211115162008.25916-1-daniel@iogearbox.net


Signed-off-by: Jakub Kicinski <kuba@kernel.org>

This reverts commit 71812af7, reversing
changes made to cc0be1ad.

Wolfram Sang says:

Please revert. Besides the driver in net, it modifies the I2C core
code. This has not been acked by the I2C maintainer (in this case me).
So, please don't pull this in via the net tree. The question raised here
(extending SMBus calls to 255 byte) is complicated because we need ABI
backwards compatibility.

Link: https://lore.kernel.org/all/YZJ9H4eM%2FM7OXVN0@shikoro/


Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Russell King says:

====================
introduce generic phylink validation

The various validate method implementations we have in phylink users
have been quite repetitive but also prone to bugs. These patches
introduce a generic implementation which relies solely on the
supported_interfaces bitmap introduced during last cycle, and in the
first patch, a bit array of MAC capabilities.

MAC drivers are free to continue to do their own thing if they have
special requirements - such as mvneta and mvpp2 which do not support
1000base-X without AN enabled. Most implementations currently in the
kernel can be converted to call phylink_generic_validate() directly
from the phylink MAC operations structure once they fill in the
supported_interfaces and mac_capabilities members of phylink_config.

This series introduces the generic implementation, and converts mvneta
and mvpp2 to use it.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

Convert mvpp2 to use phylink_generic_validate() for the bulk of its
validate() implementation. This network adapter has a restriction
that for 802.3z links, autonegotiation must be enabled.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

Convert mvneta to use phylink_generic_validate() for the bulk of its
validate() implementation. This network adapter has a restriction
that for 802.3z links, autonegotiation must be enabled.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

Add a generic validate() implementation using the supported_interfaces
and a bitmask of MAC pause/speed/duplex capabilities. This allows us
to entirely eliminate many driver private validate() implementations.

We expose the underlying phylink_get_linkmodes() function so that
drivers which have special needs can still benefit from conversion.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

CHECK   drivers/net/wan/fsl_ucc_hdlc.c
drivers/net/wan/fsl_ucc_hdlc.c:309:57: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:309:57:    expected void [noderef] __iomem *
drivers/net/wan/fsl_ucc_hdlc.c:309:57:    got restricted __be16 *
drivers/net/wan/fsl_ucc_hdlc.c:311:46: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:311:46:    expected void [noderef] __iomem *
drivers/net/wan/fsl_ucc_hdlc.c:311:46:    got restricted __be32 *
drivers/net/wan/fsl_ucc_hdlc.c:320:57: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:320:57:    expected void [noderef] __iomem *
drivers/net/wan/fsl_ucc_hdlc.c:320:57:    got restricted __be16 *
drivers/net/wan/fsl_ucc_hdlc.c:322:46: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:322:46:    expected void [noderef] __iomem *
drivers/net/wan/fsl_ucc_hdlc.c:322:46:    got restricted __be32 *
drivers/net/wan/fsl_ucc_hdlc.c:372:29: warning: incorrect type in assignment (different base types)
drivers/net/wan/fsl_ucc_hdlc.c:372:29:    expected unsigned short [usertype]
drivers/net/wan/fsl_ucc_hdlc.c:372:29:    got restricted __be16 [usertype]
drivers/net/wan/fsl_ucc_hdlc.c:379:36: warning: restricted __be16 degrades to integer
drivers/net/wan/fsl_ucc_hdlc.c:402:12: warning: incorrect type in assignment (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:402:12:    expected struct qe_bd [noderef] __iomem *bd
drivers/net/wan/fsl_ucc_hdlc.c:402:12:    got struct qe_bd *curtx_bd
drivers/net/wan/fsl_ucc_hdlc.c:425:20: warning: incorrect type in assignment (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:425:20:    expected struct qe_bd [noderef] __iomem *[assigned] bd
drivers/net/wan/fsl_ucc_hdlc.c:425:20:    got struct qe_bd *tx_bd_base
drivers/net/wan/fsl_ucc_hdlc.c:427:16: error: incompatible types in comparison expression (different address spaces):
drivers/net/wan/fsl_ucc_hdlc.c:427:16:    struct qe_bd [noderef] __iomem *
drivers/net/wan/fsl_ucc_hdlc.c:427:16:    struct qe_bd *
drivers/net/wan/fsl_ucc_hdlc.c:462:33: warning: incorrect type in argument 1 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:506:41: warning: incorrect type in argument 1 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:528:33: warning: incorrect type in argument 1 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:552:38: warning: incorrect type in argument 1 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:596:67: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:611:41: warning: incorrect type in argument 1 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:851:38: warning: incorrect type in initializer (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:854:40: warning: incorrect type in argument 1 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:855:40: warning: incorrect type in argument 1 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:858:39: warning: incorrect type in argument 1 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:861:37: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:866:38: warning: incorrect type in initializer (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:868:21: warning: incorrect type in argument 1 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:870:40: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:871:40: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:873:39: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:993:57: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:995:46: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:1004:57: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:1006:46: warning: incorrect type in argument 2 (different address spaces)
drivers/net/wan/fsl_ucc_hdlc.c:412:35: warning: dereference of noderef expression
drivers/net/wan/fsl_ucc_hdlc.c:412:35: warning: dereference of noderef expression
drivers/net/wan/fsl_ucc_hdlc.c:724:29: warning: dereference of noderef expression
drivers/net/wan/fsl_ucc_hdlc.c:815:21: warning: dereference of noderef expression
drivers/net/wan/fsl_ucc_hdlc.c:1021:29: warning: dereference of noderef expression

Most of the warnings are due to DMA memory being incorrectly handled as IO memory.
Fix it by doing direct read/write and doing proper dma_rmb() / dma_wmb().

Other problems are type mismatches or lack of use of IO accessors.

Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lkml.org/lkml/2021/11/12/647


Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>

Use the macro 'swap()' defined in 'include/linux/minmax.h' to avoid
opencoding it.

Signed-off-by: Yihao Han <hanyihao@vivo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

ARRAY_SIZE defined in <linux/kernel.h> is safer than self-defined
macros to get size of an array such as ARRAY_LEN used here. Because
ARRAY_SIZE uses __must_be_array(arr) to ensure arr is really an array.

Reported-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
Signed-off-by: Guo Zhengkui <guozhengkui@vivo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

On low-effciency embedded platforms, transmission performance is poor
due to on Bulk-out with single packet.
Adding TSO feature improves the transmission performance and reduces
the number of interrupt caused by Bulk-out complete.

Reference to module, net: usb: aqc111.

Signed-off-by: Jacky Chou <jackychou@asix.com.tw>
Signed-off-by: David S. Miller <davem@davemloft.net>

Matt Johnston says:

====================
MCTP I2C driver

This patch series adds a netdev driver providing MCTP transport over
I2C.

It applies against net-next using recent MCTP changes there, though also
has I2C core changes for review. I'll leave it to maintainers where it
should be applied - please let me know if it needs to be submitted
differently.

The I2C patches were previously sent as RFC though the only feedback
there was an ack to 255 bytes for aspeed.

The dt-bindings patch went through review on the list.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

Provides MCTP network transport over an I2C bus, as specified in
DMTF DSP0237. All messages between nodes are sent as SMBus Block Writes.

Each I2C bus to be used for MCTP is flagged in devicetree by a
'mctp-controller' property on the bus node. Each flagged bus gets a
mctpi2cX net device created based on the bus number. A
'mctp-i2c-controller' I2C client needs to be added under the adapter. In
an I2C mux situation the mctp-i2c-controller node must be attached only
to the root I2C bus. The I2C client will handle incoming I2C slave block
write data for subordinate busses as well as its own bus.

In configurations without devicetree a driver instance can be attached
to a bus using the I2C slave new_device mechanism.

The MCTP core will hold/release the MCTP I2C device while responses
are pending (a 6 second timeout or once a socket is closed, response
received etc). While held the MCTP I2C driver will lock the I2C bus so
that the correct I2C mux remains selected while responses are received.

(Ideally we would just lock the mux to keep the current bus selected for
the response rather than a full I2C bus lock, but that isn't exposed in
the I2C mux API)

This driver requires I2C adapters that allow 255 byte transfers
(SMBus 3.0) as the specification requires a minimum MTU of 68 bytes.

Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

Used to define a local endpoint to communicate with MCTP peripherals
attached to an I2C bus. This I2C endpoint can communicate with remote
MCTP devices on the I2C bus.

In the example I2C topology below (matching the second yaml example) we
have MCTP devices on busses i2c1 and i2c6. MCTP-supporting busses are
indicated by the 'mctp-controller' DT property on an I2C bus node.

A mctp-i2c-controller I2C client DT node is placed at the top of the
mux topology, since only the root I2C adapter will support I2C slave
functionality.
                                               .-------.
                                               |eeprom |
    .------------.     .------.               /'-------'
    | adapter    |     | mux  --@0,i2c5------'
    | i2c1       ----.*|      --@1,i2c6--.--.
    |............|    \'------'           \  \  .........
    | mctp-i2c-  |     \                   \  \ .mctpB  .
    | controller |      \                   \  '.0x30   .
    |            |       \  .........        \  '.......'
    | 0x50       |        \ .mctpA  .         \ .........
    '------------'         '.0x1d   .          '.mctpC  .
                            '.......'          '.0x31   .
                                                '.......'
(mctpX boxes above are remote MCTP devices not included in the DT at
present, they can be hotplugged/probed at runtime. A DT binding for
specific fixed MCTP devices could be added later if required)

Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>