FORTIFY_SOURCE detects various overflows at compile and run time.
(6974f0c4 ("include/linux/string.h:
add the option of fortified string.h functions)

ARCH_HAS_FORTIFY_SOURCE means that the architecture can be built and
run with CONFIG_FORTIFY_SOURCE.

Since mips can be built and run with that flag,
select ARCH_HAS_FORTIFY_SOURCE as default.
Signed-off-by: Dmitry Korotin <dkorotin@wavecomp.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org

CSR IPI and legacy MMIO use the same infrastructure, but CSR IPI is
faster than legacy MMIO IPI. This patch enable CSR IPI if possible
(except for MailBox, because CSR IPI is too complicated for MailBox).
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: linux-mips@vger.kernel.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: Huacai Chen <chenhuacai@gmail.com>

All Loongson-3 CPU family:

Code-name         Brand-name       PRId
Loongson-3A R1    Loongson-3A1000  0x6305
Loongson-3A R2    Loongson-3A2000  0x6308
Loongson-3A R2.1  Loongson-3A2000  0x630c
Loongson-3A R3    Loongson-3A3000  0x6309
Loongson-3A R3.1  Loongson-3A3000  0x630d
Loongson-3A R4    Loongson-3A4000  0xc000
Loongson-3B R1    Loongson-3B1000  0x6306
Loongson-3B R2    Loongson-3B1500  0x6307

Features of R4 revision of Loongson-3A:

  - All R2/R3 features, including SFB, V-Cache, FTLB, RIXI, DSP, etc.
  - Support variable ASID bits.
  - Support MSA and VZ extensions.
  - Support CPUCFG (CPU config) and CSR (Control and Status Register)
      extensions.
  - 64 entries of VTLB (classic TLB), 2048 entries of FTLB (8-way
      set-associative).

Now 64-bit Loongson processors has three types of PRID.IMP: 0x6300 is
the classic one so we call it PRID_IMP_LOONGSON_64C (e.g., Loongson-2E/
2F/3A1000/3B1000/3B1500/3A2000/3A3000), 0x6100 is for some processors
which has reduced capabilities so we call it PRID_IMP_LOONGSON_64R
(e.g., Loongson-2K), 0xc000 is supposed to cover all new processors in
general (e.g., Loongson-3A4000+) so we call it PRID_IMP_LOONGSON_64G.
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: linux-mips@vger.kernel.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: Huacai Chen <chenhuacai@gmail.com>

Loongson-3A R4+ (Loongson-3A4000 and newer) has CPUCFG (CPU config) and
CSR (Control and Status Register) extensions. This patch add read/write
functionalities for them.
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: linux-mips@vger.kernel.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: Huacai Chen <chenhuacai@gmail.com>

The memory initialization of SGI-IP27 is already half-way to support
SPARSEMEM. It only had free_bootmem_with_active_regions() left-overs
interfering with sparse_memory_present_with_active_regions().

Replace these calls with simpler memblocks_present() call in prom_meminit()
and adjust arch/mips/Kconfig to enable SPARSEMEM and SPARSEMEM_EXTREME for
SGI-IP27.
Co-developed-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

When Loongson3 LL/SC errata workarounds are enabled (ie.
CONFIG_CPU_LOONGSON3_WORKAROUNDS=y) run a tool to scan through the
compiled kernel & ensure that the workaround is applied correctly. That
is, ensure that:

  - Every LL or LLD instruction is preceded by a sync instruction.

  - Any branches from within an LL/SC loop to outside of that loop
    target a sync instruction.

Reasoning for these conditions can be found by reading the comment above
the definition of __SYNC_loongson3_war in arch/mips/include/asm/sync.h.

This tool will help ensure that we don't inadvertently introduce code
paths that miss the required workarounds.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

In ejtag_debug_handler() we must reload the address of
ejtag_debug_buffer_spinlock if an sc fails, since the address in k0 will
have been clobbered by the result of the sc instruction. In the case
where we simply load a non-zero value (ie. there's contention for the
lock) the address will not be clobbered & we can simply branch back to
repeat the load from memory without reloading the address into k0.

The primary motivation for this change is that it moves the target of
the bnez instruction to an instruction within the LL/SC loop (the LL
itself), which we know contains no other memory accesses & therefore
isn't affected by Loongson3 LL/SC errata.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

In ejtag_debug_handler we use LL & SC instructions to acquire & release
an open-coded spinlock. For Loongson3 systems affected by LL/SC errata
this requires that we insert a sync instruction prior to the LL in order
to ensure correct behavior of the LL/SC loop.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Loongson3 systems with CONFIG_CPU_LOONGSON3_WORKAROUNDS enabled already
emit a full completion barrier as part of the inline assembly containing
LL/SC loops for atomic operations. As such the barrier emitted by
__smp_mb__before_atomic() is redundant, and we can remove it.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

The loongson_llsc_mb() macro is no longer used - instead barriers are
emitted as part of inline asm using the __SYNC() macro. Remove the
now-defunct loongson_llsc_mb() macro.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Generate the sync instructions required to workaround Loongson3 LL/SC
errata within inline asm blocks, which feels a little safer than doing
it from C where strictly speaking the compiler would be well within its
rights to insert a memory access between the separate asm statements we
previously had, containing sync & ll instructions respectively.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Generate the sync instructions required to workaround Loongson3 LL/SC
errata within inline asm blocks, which feels a little safer than doing
it from C where strictly speaking the compiler would be well within its
rights to insert a memory access between the separate asm statements we
previously had, containing sync & ll instructions respectively.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

When building a kernel configured to support Loongson3 LL/SC workarounds
(ie. CONFIG_CPU_LOONGSON3_WORKAROUNDS=y) the inline assembly in
__xchg_asm() & __cmpxchg_asm() already emits completion barriers, and as
such we don't need to emit extra barriers from the xchg() or cmpxchg()
macros. Add compile-time constant checks causing us to omit the
redundant memory barriers.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Generate the sync instructions required to workaround Loongson3 LL/SC
errata within inline asm blocks, which feels a little safer than doing
it from C where strictly speaking the compiler would be well within its
rights to insert a memory access between the separate asm statements we
previously had, containing sync & ll instructions respectively.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Use smp_mb__before_atomic() rather than smp_mb__before_llsc() in
test_and_set_bit(), test_and_clear_bit() & test_and_change_bit(). The
_atomic() versions make semantic sense in these cases, and will allow a
later patch to omit redundant barriers for Loongson3 systems that
already include a barrier within __test_bit_op().
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Generate the sync instructions required to workaround Loongson3 LL/SC
errata within inline asm blocks, which feels a little safer than doing
it from C where strictly speaking the compiler would be well within its
rights to insert a memory access between the separate asm statements we
previously had, containing sync & ll instructions respectively.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Rather than using custom SZLONG_LOG & SZLONG_MASK macros to shift & mask
a bit index to form word & bit offsets respectively, make use of the
standard BIT_WORD() & BITS_PER_LONG macros for the same purpose.

volatile is added to the definition of pointers to the long-sized word
we'll operate on, in order to prevent the compiler complaining that we
cast away the volatile qualifier of the addr argument. This should have
no effect on generated code, which in the LL/SC case is inline asm
anyway & in the non-LLSC case access is constrained by compiler barriers
provided by raw_local_irq_{save,restore}().
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Introduce __bit_op() & __test_bit_op() macros which abstract away the
implementation of LL/SC loops. This cuts down on a lot of duplicate
boilerplate code, and also allows R10000_LLSC_WAR to be handled outside
of the individual bitop functions.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

The IRQ-disabling non-LLSC fallbacks for bitops on UP systems already
return a zero or one, so there's no need to perform another comparison
against zero. Move these comparisons into the LLSC paths to avoid the
redundant work.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Use the BIT() macro in asm/bitops.h rather than open-coding its
equivalent.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

The logical operations or & xor used in the test_and_set_bit_lock(),
test_and_clear_bit() & test_and_change_bit() functions currently force
the value 1<<bit to be placed in a register. If the bit is compile-time
constant & fits within the immediate field of an or/xor instruction (ie.
16 bits) then we can make use of the ori/xori instruction variants &
avoid the use of an extra register. Add the extra "i" constraints in
order to allow use of these immediate encodings.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

The only difference between test_and_set_bit() & test_and_set_bit_lock()
is memory ordering barrier semantics - the former provides a full
barrier whilst the latter only provides acquire semantics.

We can therefore implement test_and_set_bit() in terms of
test_and_set_bit_lock() with the addition of the extra memory barrier.
Do this in order to avoid duplicating logic.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

The start position for an ins instruction is always encoded as an
immediate, so allowing registers to be used by the inline asm makes no
sense. It should never happen anyway since a bit index should always be
small enough to be treated as an immediate, but remove the nonsensical
"r" for sanity.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Rather than #ifdef on CONFIG_CPU_* to determine whether the ins
instruction is supported we can simply check MIPS_ISA_REV to discover
whether we're targeting MIPSr2 or higher. Do so in order to clean up the
code.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

set_bit() can set bits 0-15 using an ori instruction, rather than
loading the value -1 into a register & then using an ins instruction.

That is, rather than the following:

  li   t0, -1
  ll   t1, 0(t2)
  ins  t1, t0, 4, 1
  sc   t1, 0(t2)

We can have the simpler:

  ll   t1, 0(t2)
  ori  t1, t1, 0x10
  sc   t1, 0(t2)

The or path already allows immediates to be used, so simply restricting
the ins path to bits that don't fit in immediates is sufficient to take
advantage of this.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Reorder conditions in our various bitops functions that check
kernel_uses_llsc such that they handle the !kernel_uses_llsc case first.
This allows us to avoid the need to duplicate the kernel_uses_llsc check
in all the other cases. For functions that don't involve barriers common
to the various implementations, we switch to returning from within each
if block making each case easier to read in isolation.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Remove the remaining duplication between 32b & 64b in asm/atomic.h by
making use of an ATOMIC_OPS() macro to generate:

  - atomic_read()/atomic64_read()
  - atomic_set()/atomic64_set()
  - atomic_cmpxchg()/atomic64_cmpxchg()
  - atomic_xchg()/atomic64_xchg()

This is consistent with the way all other functions in asm/atomic.h are
generated, and ensures consistency between the 32b & 64b functions.

Of note is that this results in the above now being static inline
functions rather than macros.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Unify the definitions of atomic_sub_if_positive() &
atomic64_sub_if_positive() using a macro like we do for most other
atomic functions. This allows us to share the implementation ensuring
consistency between the two. Notably this provides the appropriate
loongson3_war barriers in the atomic64_sub_if_positive() case which were
previously missing.

The code is rearranged a little to handle the !kernel_uses_llsc case
first in order to de-indent the LL/SC case & allow us not to go over 80
characters per line.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Use smp_mb__before_atomic() & smp_mb__after_atomic() in
atomic_sub_if_positive() rather than the equivalent
smp_mb__before_llsc() & smp_llsc_mb(). The former are more standard &
this preps us for avoiding redundant duplicate barriers on Loongson3 in
a later patch.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Generate the sync instructions required to workaround Loongson3 LL/SC
errata within inline asm blocks, which feels a little safer than doing
it from C where strictly speaking the compiler would be well within its
rights to insert a memory access between the separate asm statements we
previously had, containing sync & ll instructions respectively.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Cut down on duplication by generalizing the ATOMIC_OP(),
ATOMIC_OP_RETURN() & ATOMIC_FETCH_OP() macros to work for both 32b &
64b atomics, and removing the ATOMIC64_ variants. This ensures
consistency between our atomic_* & atomic64_* functions.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Handle the !kernel_uses_llsc path first in our ATOMIC_OP(),
ATOMIC_OP_RETURN() & ATOMIC_FETCH_OP() macros & return from within the
block. This allows us to de-indent the kernel_uses_llsc path by one
level which will be useful when making further changes.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

We define macros in asm/atomic.h which end each line with space
characters before a backslash to continue on the next line. Remove the
space characters leaving tabs as the whitespace used for conformity with
coding convention.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Use the new __SYNC() infrastructure to implement sync_ginv(), for
consistency with much of the rest of the asm/barrier.h.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Implement __sync() using the new __SYNC() infrastructure, which will
take care of not emitting an instruction for old R3k CPUs that don't
support it. The only behavioral difference is that __sync() will now
provide a compiler barrier on these old CPUs, but that seems like
reasonable behavior anyway.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

The definition of fast_mb() is the same in both the Octeon & non-Octeon
cases, so remove the duplication & define it only once.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

We #ifdef on Cavium Octeon CPUs, but emit the same sync instruction in
both cases. Remove the #ifdef & simply expand to the __sync() macro.

Whilst here indent the strong ordering case definitions to match the
indentation of the weak ordering ones, helping readability.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Simplify our definitions of rmb() & wmb() using the new __SYNC()
infrastructure.

The fast_rmb() & fast_wmb() macros are removed, since they only provided
a level of indirection that made the code less readable & weren't
directly used anywhere in the kernel tree.

The Octeon #ifdef'ery is removed, since the "syncw" instruction
previously used is merely an alias for "sync 4" which __SYNC() will emit
for the wmb sync type when the kernel is configured for an Octeon CPU.
Similarly __SYNC() will emit nothing for the rmb sync type in Octeon
configurations.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

Introduce an asm/sync.h header which provides infrastructure that can be
used to generate sync instructions of various types, and for various
reasons. For example if we need a sync instruction that provides a full
completion barrier but only on systems which have weak memory ordering,
we can generate the appropriate assembly code using:

  __SYNC(full, weak_ordering)

When the kernel is configured to run on systems with weak memory
ordering (ie. CONFIG_WEAK_ORDERING is selected) we'll emit a sync
instruction. When the kernel is configured to run on systems with strong
memory ordering (ie. CONFIG_WEAK_ORDERING is not selected) we'll emit
nothing. The caller doesn't need to know which happened - it simply says
what it needs & when, with no concern for checking the kernel
configuration.

There are some scenarios in which we may want to emit code only when we
*didn't* emit a sync instruction. For example, some Loongson3 CPUs
suffer from a bug that requires us to emit a sync instruction prior to
each ll instruction (enabled by CONFIG_CPU_LOONGSON3_WORKAROUNDS). In
cases where this bug workaround is enabled, it's wasteful to then have
more generic code emit another sync instruction to provide barriers we
need in general. A __SYNC_ELSE() macro allows for this, providing an
extra argument that contains code to be assembled only in cases where
the sync instruction was not emitted. For example if we have a scenario
in which we generally want to emit a release barrier but for affected
Loongson3 configurations upgrade that to a full completion barrier, we
can do that like so:

  __SYNC_ELSE(full, loongson3_war, __SYNC(rl, always))

The assembly generated by these macros can be used either as inline
assembly or in assembly source files.

Differing types of sync as provided by MIPSr6 are defined, but currently
they all generate a full completion barrier except in kernels configured
for Cavium Octeon systems. There the wmb sync-type is used, and rmb
syncs are omitted, as has been the case since commit 6b07d38a
("MIPS: Octeon: Use optimized memory barrier primitives."). Using
__SYNC() with the wmb or rmb types will abstract away the Octeon
specific behavior and allow us to later clean up asm/barrier.h code that
currently includes a plethora of #ifdef's.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

When targeting MIPSr6 or higher make use of a compact branch in LL/SC
loops, preventing the insertion of a delay slot nop that only serves to
waste space.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org