In the microMIPS encoding some memory access instructions have their
immediate offset reduced to 12 bits only. That does not match the GCC
`R' constraint we use in some places to satisfy the requirement,
resulting in build failures like this:
{standard input}: Assembler messages:
{standard input}:720: Error: macro used $at after ".set noat"
{standard input}:720: Warning: macro instruction expanded into multiple instructions
Fix the problem by defining a macro, `GCC_OFF12_ASM', that expands to
the right constraint depending on whether microMIPS or standard MIPS
code is produced. Also apply the fix to where `m' is used as in the
worst case this change does nothing, e.g. where the pointer was already
in a register such as a function argument and no further offset was
requested, and in the best case it avoids an extraneous sequence of up
to two instructions to load the high 20 bits of the address in the LL/SC
loop. This reduces the risk of lock contention that is the higher the
more instructions there are in the critical section between LL and SC.
Strictly speaking we could just bulk-replace `R' with `ZC' as the latter
constraint adjusts automatically depending on the ISA selected.
However it was only introduced with GCC 4.9 and we keep supporing older
compilers for the standard MIPS configuration, hence the slightly more
complicated approach I chose.
The choice of a zero-argument function-like rather than an object-like
macro was made so that it does not look like a function call taking the
C expression used for the constraint as an argument. This is so as not
to confuse the reader or formatting checkers like `checkpatch.pl' and
follows previous practice.
Signed-off-by: Maciej W. Rozycki <macro@codesourcery.com>
Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8482/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
With binutils 2.24 the attempt to switch with microMIPS mode to MIPS III
mode through .set mips3 results in *lots* of warnings like
{standard input}: Assembler messages:
{standard input}:397: Warning: the 64-bit MIPS architecture does not support the `smartmips' extension
during a kernel build. Fixed by using .set arch=r4000 instead.
This breaks support for building the kernel with binutils 2.13 which
was supported for 32 bit kernels only anyway and 2.14 which was a bad
vintage for MIPS anyway.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Having received another series of whitespace patches I decided to do this
once and for all rather than dealing with this kind of patches trickling
in forever.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Fix the following build breakage in v3.4-rc1:
CC kernel/irq_work.o
In file included from include/linux/irq_work.h:4:0,
from kernel/irq_work.c:10:
include/linux/llist.h: In function 'llist_del_all':
include/linux/llist.h:178:2: error: implicit declaration of function 'BUILD_BUG_ON' [-Werror=implicit-function-declaration]
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3568/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
It was a nice optimization - on paper at least. In practice it results in
branches that may exceed the maximum legal range for a branch. We can
fight that problem with -ffunction-sections but -ffunction-sections again
is incompatible with -pg used by the function tracer.
By rewriting the loop around all simple LL/SC blocks to C we reduce the
amount of inline assembler and at the same time allow GCC to often fill
the branch delay slots with something sensible or whatever else clever
optimization it may have up in its sleeve.
With this optimization gone we also no longer need -ffunction-sections,
so drop it.
This optimization was originally introduced in 2.6.21, commit
5999eca25c1fd4b9b9aca7833b04d10fe4bc877d (linux-mips.org) rsp.
f65e4fa8e0 (kernel.org).
Original fix for the issues which caused me to pull this optimization by
Paul Gortmaker <paul.gortmaker@windriver.com>.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Replace some instances of smp_llsc_mb() with a new macro
smp_mb__before_llsc(). It is used before ll/sc sequences that are
documented as needing write barrier semantics.
The default implementation of smp_mb__before_llsc() is just smp_llsc_mb(),
so there are no changes in semantics.
Also simplify definition of smp_mb(), smp_rmb(), and smp_wmb() to be just
barrier() in the non-SMP case.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/851/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
On some CPUs, it is more efficient to disable and enable interrupts in the
kernel rather than use ll/sc for atomic operations. But if we were to set
cpu_has_llsc to false, we would break the userspace futex interface (in
asm/futex.h).
We separate the two concepts, with a new predicate kernel_uses_llsc, that
lets us disable the kernel's use of ll/sc while still allowing the futex
code to use it.
Also there were a couple of cases in bitops.h where we were using ll/sc
unconditionally even if cpu_has_llsc were false.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Maciej W. Rozycki